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ELECTRO-METALLURGY 


Frontispiece 


GRAMMES    EL^CTROTYI'ING    MAGNETO-ELECTRIC    MACI  INE 


THE    ART 

OF 

ELECTRO-METALLURGY 

INCLUDING    ALL    KNOWN    PROCESSES    OF 
ELECTRO-DEPOSITION 


BY    G.    GORE,    LL.D,    F.R.S. 


SECOND    EDITION 


D.    APPLE  TON     AND     CO. 

NEW    YORK 

1884 


ft 


INTRODUCTION. 


HAVING  been  asked  by  the  publishers  of  the  Text- 
books of  Science,  to  write  a  small  volume  on  the 
subject  of  Electro-metallurgy,  I  have  endeavoured 
to  produce  such  a  book  as  would  be  useful  to  scientific 
students,  to  practical  workers  in  the  art  of  electro- 
metallurgy, gilders,  platers,  &c.,  and  to  all  persons  who 
wish  to  obtain  in  a  compact  form,  an  explanation  of 
the  principles  and  facts  upon  which  the  art  of  electro- 
metallurgy is  based,  the  circumstances  under  which 
nearly  every  known  metal  is  deposited,  and  the  special 
details  of  technical  workshop  manipulation  in  the 
galvano-plastic  art  I  have  also  given  an  historical 
sketch  of  the  development  of  the  subject,  arranged  in 
chronological  order. 

The  book  is  divided  essentially  into  four  parts, 
viz.,  First,  the  Historical  sketch,  showing  how  from 
one  or  two  isolated,  and  apparently  unimportant  facts, 
the  great  subject  of  Electro-chemistry  arose,  and  by 
the  incessant,  and  unremunerated  labours  of  many 

6G5386 


viii  Introduction. 

eminent  scientific  investigators,  and  the  exertions  of 
practical  operators,  it  has  gradually  extended,  until 
nearly  every  known  metal  has  been  separated,  copper 
has  been  deposited  in  great  quantities,  and  the  emi- 
nently useful,  and  beautiful  products  of  artistic 
electro-deposition,  have  spread  nearly  all  over  the 
Earth,  and  are  to  be  found  in  every  civilised  home. 
The  Second  part  consists  of  the  Theoretical  division, 
being  a  concise  statement  of  the  chief  facts  and  prin- 
ciples upon  which  the  practical  art  is  based,  together 
with  descriptions  of  the  classes  of  phenomena  usually 
met  with  in  electrolytic  and  electro-depositing  pro- 
cesses ;  the  facts  and  principles  being  arranged  in  as 
systematic  and  logical  an  order  as  I  could  place  them. 
The  Third  part  (section  A)  is  the  first  portion  of  the 
Practical  division  of  the  book  ;  and  treats  of  the  general 
methods  of  deposition,  the  selection  of  depositing  pro- 
cesses, the  general  rules  to  be  obeyed,  and  points  to 
be  observed,  in  actual  working  with  all  metals,  followed 
by  the  special  means  of  depositing  nearly  every  known 
metal  and  metalloid.  The  metals,  &c.,  are  arranged 
in  their  ordinary  chemical  classes  in  the  following 
order  : — Electro-negative  or  brittle  metals,  noble,  base, 
earth  and  alkaline  earth,  alkali  metals,  and  finally  the 
metalloids  ;  and  the  arrangement  is  such,  that  every 
known  instance  of  the  electro-deposition  of  nearly 
every  known  metal,  and  metalloid,  may  be  readily 
found  and  referred  to.  It  is  hoped  that  not  only 
students  and  practical  workers  in  the  art,  will  find  this 


Introduction.  ix 

section  of  value  to  them,  but  that  even  scientific 
investigators  may  find  it  useful  for  reference.  The 
Fourth  (or  concluding)  section,  B  is  of  a  more  special 
and  technical  character,  and  has  been  composed 
almost  entirely  for  the  use  of  practical  operators, 
including  those  who  have  not  had  the  advantage  of 
chemical  instruction :  it  contains  a  variety  of  tech- 
nical points  of  instruction  necessary  for  the  successful 
prosecution  of  the  art, — information  which  could  not 
be  so  conveniently  classed  or  supplied  in  the  preceding 
sections.  This  part  also  includes  a  list  of  all  the 
books  published  on  the  subject,  and  an  extensive  and 
almost  complete  list  of  the  English  Patents  (nearly 
300  in  number)  relating  to  electro-deposition,  taken 
out  from  the  earliest  period  of  the  art,  until  the  present 
time. 

I  have  endeavoured  not  only  to  make  the  book  a 
treatise  on  the  practical  art  of  Electro-metallurgy,  but 
also  to  include  an  outline  of  the  science  of  electro- 
chemistry, upon  which  that  art  is  based  ;  and  I  have 
also  spared  no  trouble  in  order  to  make  it  as 
perfect  as  I  could  ;  the  most  complete  portions  are 
those  which  treat  of  the  common  methods  of  silvering, 
gilding,  moulding ;  the  deposition  of  copper,  nickel, 
brass,  iron,  and  tin  ;  the  special  details  of  the  art  ; 
and  the  accounts  of  such  experiments  and  processes 
with  the  less  common  metals,  as  scientific  investiga- 
tors and  practical  inventors,  may  be  likely  to  further 
examine,  or  practically  apply. 


x  Introduction. 

Numerous  experiments  of  my  own  on  the  subject, 
(many  of  them,  through  want  of  previous  opportunity, 
being  now  for  the  first  time  published),  are  scattered 
through  the  first  part  of  the  Practical  section  of  the 
book  ;  a  few  of  them  being  made  to  fill  up  missing 
links,  whilst  the  book  was  in  progress.  I  had  hoped 
also  to  have  made  others  in  a  similar  way,  for  the 
purpose  of  settling  some  debateable  questions  still 
remaining ;  for  instance,  to  determine  whether  alumi- 
nium is,  or  is  not,  capable  of  being  deposited  from  an 
aqueous  solution  ;  but,  owing  to  the  deficiency  of  en- 
couragement of  original  scientific  research  in  this 
country,  I  have  been  deterred  from  so  doing. 

I  beg  to  express  my  indebtedness  to  Mr.  E.  W. 
BALL,  and  to  my  colleague,  Mr.  A.  BRUCE,  F.C.S.,  for 
the  assistance  they  have  kindly  rendered  me  in  cor- 
recting the  proof-sheets. 

GEORGE  GORE. 

Birmingham,  1877. 


CONTENTS. 


HISTORICAL   SKETCH. 

TAGff 

Earliest  known  facts  of  Electro-metallurgy        .            .            .  i 

Volta's  discovery  of  Chemical  Electricity,  1799        ...  2 

Decomposition  of  Water  by  Nicholson  and  Carlisle,  1800        .             .  2 
Electrolytic  transfer  of  Acids  and  Alkalies.     Hisinger  and  Berzelius, 

1803                                      3 

Electro-deposition  of  Metals.     Cruikshank,  1804          .  .  .3 

Electro-gilding  by  a  separate  Current.     Brugnatelli,  1805  •             •  3 

Electro-deposition  of  the  Alkali-metals.     H.  Davy,  1807         .             .  3 

Thermo-electricity.     Seebeck.     1812            ....  4 

Electro-chromy.     Nobili,  1826  ......  4 

Magneto-electricity.     Faraday,  1831            ....  4 

Definite  Electro-chemical  Action.     Faraday,  1834        .  .  .4 

Copying  Surfaces  in  Copper.     De  la  Rue,  1836      ...  4 

.,             .,             ,,            Jacobi,  Spencer,  Jordan,  1839  .            .  5 

Mr.  Jordan's  Paper  on  Electrotype  ....             .             .  5 

Mr.  Spencer's  Paper  on  Electrotype      .....  7 

The  single-cell  apparatus      ......  18 

Gilding  by  Simple  Immersion  ;  Elkington's  Process,  1838                    .  19 

,,          contact  with  zinc            ,,             ,,             ,,           .  19 

First  employment  of  Alkaline  Cyanides.    Dr.  Wright,  De  Ruolz,  1840  21 

Rendering  Surfaces  conducting  by  means  of  Blacklead.     Mr.  Murray  23 

Deposition  by  means  of  a  separate  Battery-current.     Mr.  Mason         .  23 

Mr.  Smee's  Experiments  in  Electro-deposition,  1841           .             .  25 

Electro-deposition  of  Brass.     De  Ruolz,  1841  .             .             .  25 

Deposition  by  Magneto-electricity.     Woolrich,  1842           .             .  25 

Palmer's  Process  of  Glyphography,  1842           .             .             .  25 

Application  of  Thermo-electricity  to  Plating,  1843  ...  26 

Discovery  of  Bright  Silver  deposition.     Milward,  1847             .            .  26 

Subsequent  advances  in  the  Subject.            ....  27 


xiv  Contents. 

Deposition  of  Individual  Substances — continued 

CLASS  II.     Electro-negative  or  Brittle  Metals. 

PAGE 

2.  Deposition  of  Arsenic           .            .            .            .  97 

,,                      ,,       by  Simple  Immersion  Process    .  .       98 

,,                      „       by  Contact  with  another  Metal         .  98 

,,                               by  Separate  Current  Process      .  .      98 

3.  Deposition  of  Tellurium       •.           •.           •.             .            .  98 

4.  Deposition  of  Antimony,  Crystalline  and  Amorphous  .  .       99 

,,                      ,,         by  Simple  Immersion  Process        .  101 

,,                      ,,         by  Separate  Current       ,,         .  .     102 

,,               explosive  Antimony   ....  103 

5.  Deposition  of  Bismuth    .            .            .            .            .  .     in 

,,                    ,,         by  Simple  Immersion  Process         .  in 

,,                   ,,        by  Separate  Current      „          .  .112 

CLASS  III.    Noble  Metals. 

6.  Deposition  of  Osmium           .            .            .            .            .  113 

7.  Deposition  of  Ruthenium  .....     113 

8.  Deposition  of  Rhodium         .  .  .  .  .113 

9.  Deposition  of  Iridium    .              .            .            .            .  .114 

10.  Deposition  of  Palladium        .  .  .  .  .1141 

Electrolysis  of  Anhydrous  Hydrofluoric  acid  .            .  .115 

11.  Deposition  of  Platinum          .....  118 

,,         by  Simple  Immersion  Process           .            .  .     n9 

,,         by  Separate  Current       ,,            .            .            .  iigj 

12.  Deposition  of  Gold          ......     122 

Preparation  of  Salts  of  Gold  ....  122 

Electrolysis  of  Fluorides  with  a  gold  anode  .  .  .  126 

Solutions  for  Electro-gilding  ....  127 

Gilding  by  Simple  Immersion  Process      .            .  .     127 

,,         ,,    Contact  with  Zinc .             ...  130 

Gold  Solutions  for  Separate  Current  Process  .            .  .130 

Gilding  Solution  of  M.  de  Ruolz  and  others  .  .  132 

Making  Gilding  Solutions  by  Battery  Process  .  .  133 

Cold  Solutions  for  gilding  by  Separate  Current  Process  .  134 

Hot  „  „  „  „  „  •  136 

Coloured  Gilding  ....  138 

Necessity  of  free  Cyanide  ...  .  140 

Management  of  Gilding  Solutions  .  141 

Gilding  Base  Metals  ...  .142 

Gilding  the  insides  of  Vessels  .  143 

Ungilding  articles  of  Silver  and  Iron  .  .  143 

Recovery  of  Gold  from  Wash-water  .  .  .  144 

,  ,,  Cyanide  Solutions  .  .  .  144 

Recovering  Gold  or  Silver,  by  M.  Bolley  .  145 


Contents.  xv 

Deposition  of  Individual  Substances — continued  PAGE 

13.  Deposition  of  Silver  .             .            .            .             .  146 

Preparation  of  Salts  of  Silver  .....  147 

Chemical  characters  of  Cyanide  of  Silver  .             .            .  148 

Electrolysis  of  Salts  of  Silver    .....  149 

Deposition  of  Silver  by  Simple  Immersion  Process            .  151 

Silvering  by  Simple  Immersion  Process  .  .  .152 

,,         ,,      Contact  with  Zinc       .             .             .             .  155 

Solutions  for  Silvering  by  means  of  a  separate  Current           .  155 

Making  Cyanide  of  Silver  Solution  by  Chemical  Means  156 
How  to  Electro-plate  over  soft  solder              .             .             .164 

Making  Cyanide  of  Silver  Solution  by  the  Battery  Method  165 

Condensed  outline  of  the  French  Silver-plating  Process         .  166 

Deposition  of  Bright  Silver             ....  167 

Vats  for  containing  Silver  Solutions     ....  169 

Quality  of  Electro-deposited  Silver             .             .            .  171 

Management  of  Silver-plating  Liquids             .             .             .  172 

Rapidity  of  Deposition  of  Silver    ....  178 

Thickness  of  Deposited  Silver              ....  178 

Ornamenting  Silver-plated  Articles            .             .             .  180 
Dead  Silver,  Oxidised  Silver,  Nielled  Silver    .            .            .180 

Cleaning  articles  of  Silver   .             ...            .            .  182 

'Stripping' Plated  Articles      .  .  .  .  .183 

Analysis  of  Cyanide  of  Silver  plating  Solution       .            .  184 

Recovery  of  Silver  and  Gold  from  Residuary  Liquids             .  187 

Extraction  of  Silver  by  the  Wet  Method    .             .            .  191 

»,                  ,,                Dry        ,,                .-.-,.             .  192 

Recovery  of  Gold  by  the  Wet  Method      .            .            .  192 

Dry      ,,                    ...  193 

Testing  the  Purity  of  Silver             ....  194 

14.  Deposition  of  Mercury    ......  195 

Ordinary  Salts  of  Mercury              ....  195 

Deposition  of  Mercury  by  Simple  Immersion  Process             .  196 

Electrolysis  of  Salts  of  Mercury      ....  196 

Electrolytic  vibrations  and  sounds       ....  197 


CLASS  IV.    Base  Metals. 

15.  Deposition  of  Copper     .  .  .  .  .  .198 

Common  Salts  of  Copper  .....  198 

Electrical  relations  of  Copper  .....  199 

Deposition  of  Copper  by  Simple  Immersion  Process          .  199 

Electrolysis  of  Salts  of  Copper             ....  200 

Applications  of  Electro-deposition  of  Copper        .            .  202 

Coppering  Articles  by  Simple  Immersion  Process       .            .  202 


xvi  Contents. 

Deposition  of  Individual  Substances — continued  PAGE 

Separation  of  Copper  from  Cupriferous  Liquids  .  .  203 

Deposition  of  Copper  by  contact  with  another  Metal  .  204 

,,  ,,  ,,  Single-cell  Process  .  .  205 

Coppering  Iron  Cylinders  for  Calico-printing  .  .  205 

Deposition  of  Copper  by  the  Separate  Current  Process  .  206 

Depositing  Copper  upon  Metals  generally  .  .  .  206 

,,  ,,  ,,  Zinc,  Iron,  etc.  .  .  .  207 
Management  of  Coppering  Liquids  ....  209 

Rapidity  and  cost  of  Electro-depositing  Copper  .  .  210 

Composition  of  the  Dirt  upon  Copper  Anodes  .  .  210 

Refining  crude  Copper  by  Electrolysis  .  .  .  212 

Estimation  of  Copper  in  Solutions  by  Electrolysis  .  .  213 

Preventing  Adhesion  of  Deposited  Copper  to  Surfaces  .  214 

Copying  Engraved  Metal  Plates  in  Copper  .  .  .214 

,,  Daguerreotype  pictures  ,,  .  .  215 
Coating  Cloth  with  Copper  .....  216 

Depositing  Copper  upon  Non-metallic  Surfaces  .  .  216 

Rendering  Non-metallic  Surfaces  Conductive  .  .217 

Coppering  Lamp-posts,  Ornamental  Ironwork,  etc.  .  221 

Coppering  Fruit,  Flowers,  Insects,  etc.  .  .  .221 

Coating  Plaster  models  and  Clay  figures  with  Copper  .  222 

Copying  Wood  engravings  in  Copper  .  .  .  222 

, ,         set-up  Type                 , ,                 .            .  .          223 

Moulding  and  Copying  Coins,  etc.,  in  Copper            .  .     224 

Elastic  Moulding  Composition       ....  227 

Copying  Busts,  Statuettes,  Statues,  etc.          .            .  .227 

Glyphography         .            .            .            .            .  .          231 

Etching  Copper  Plates  by  Electrolysis  .  .  .231 

Depositing  Copper  upon  Glass,  Porcelain,  etc.  .  .  232 

16.  Deposition  of  Nickel      ......     232 

Ordinary  Salts  of  Nickel     ....  232 

Electrolysis  of  Nickel  Solutions  ....     232 

Deposition  of  Nickel  by  the  Simple  Immersion  Process  .           235 

*   ,,                ,,     by  Contact  with  another  Metal  .     236 

,,                ,,      by  Separate  Current  Process  .           236 

Management  of  Nickel  Solutions         ....     238 

Properties  and  uses  of  Electro-deposited  Nickel    .  240 

Estimation  of  Nickel  by  means  of  Electrolysis  .     240 

17.  Deposition  of  Cobalt              .  241 

Ordinary  Salts  of  Cobalt          .            .            .  .241 

Electrolysis  of  Cobalt  Solutions      .  242 

Deposition  of  Cobalt  by  Contact  with  another  Metal  .     242 

,,            ,,       Separate  Current  Process  .           242 

18.  Deposition  of  Iron  ......     243 

Common  Salts  of  Iron                    .            .           •  243 


Contents.  xvii 

Deposition  of  Individual  Substances— continued.  PAGE 

Deposition  of  Iron  by  Simple  Immersion  Process       .  .     244 

Electrolysis  of  Salts  of  Iron             .             .             .  244 

Coating  Engraved  Copper  Plates  with  Iron    .             .  .     246 

Management  of  Solutions  for  Depositing  Iron      .  248 

Properties  and  uses  of  Electro-deposited  Iron             .  .     248 

19.  Deposition  of  Manganese      ....  249 

Common  Salts  of  Manganese  .....     250 

Deposition  of  Manganese  by  Simple  Immersion  Process  .  250 
Electrolysis  of  Salts  of  Manganese       ....     250 

20.  Deposition  of  Chromium       .             .             .  252 

Common  Salts  of  Chromium    .....     252 

Deposition  of  Chromium  by  Simple  Immersion  Process   .  252 

,,               ,,               by  a  Separate  Current          .  .     253 

21.  Uranium        .......  253 

Ordinary  Salts  of     ,,                ...  •     253 

Electrolysis  of  Uranium  Solutions              .  254 

22.  Tungsten  .......     255 

Electrolysis  of  Salts  of  Tungsten    .  .  .  .255 

23.  Molybdenum       .......     255 

Ordinary  Salts  of                             .            .             .            .  255 

Electrolysis  of  Molybdic  Acid  .                         .            .  .     256 

24.  Vanadium      .......  257 

Electrolysis  of  Vanadic  Acid    .            .            .            .  .257 

25.  Deposition  of  Lead    ....                         •  257 

Common  Salts  of  Lead  .....     257 

Deposition  of  Lead  by  Simple  Immersion  Process            .  257 

,,            ,,            ,,      Contact  with  a  Second  Metal  .     258 

,,            ,,            ,,      a  Separate  Current             .            .  259 

„         of  Peroxide  of  Lead  upon  Anodes            .  .     260 

Electro-chromy        .            .             .            .            .  261 

26.  Deposition  of  Thallium  ....  .     262 

Electrolysis  o&  Salts  of  Thallium     ....  262 

27.  Deposition  of  Indium     ....  •     262 

28.  Deposition  of  Tin      .....  263 

Common  Salts  of  Tin  ....  .263 

Electrical  relations  of  Tin  and  Iron            .                         .  264 

Depositing  Tin  by  Simple  Immersion  Process  .     265 

Contact  with  a  Second  Metal  .            .  267 

Electrolysis  of  Salts  of  Tin       .            .            .             .  .268 

Deposition  of  Tin  by  Separate  Current  Process     .  270 

,,          „      Alloys  of  Tin  and  Copper          .             .  •     272 

29.  Deposition  of  Cadmium         .            .  273 

Common  Salts  of  Cadmium     .             .  -     273 

Deposition  of  Cadmium  by  contact  with  another  Metal    .  273 

„            ,,             ,,          Separate  Current  Process  .     273 


xviil  Contents. 

Deposition  of  Individual  Substances — continued  PAGE 

30.  Deposition  of  Zinc          ......  274 

Common  Salts  of  Zinc        .            .            .                         .  274 

Deposition  of  Zinc  by  Simple  Immersion  Process       .            .  275 

„            ,,            ,,     Contact  with  another  Metal            .  276 

,,            ,,            ,,     Separate  Current  Process         .            .  276 

Estimation  of  Zinc  by  means  of  Electrolysis          .            .  278 

Deposition  of  Alloys  of  Zinc  and  Copper        .            .            .  278 

Solutions  for  Electro-depositing  Brass       .            .            .  279 

Electro-deposition  of  German-silver    ....  285 

Separation  of  Copper  and  Zinc  by  Electrolysis      .            .  285 


CLASS  V.    Earth  and  Alkaline  Earth  Metals. 

31.  Deposition  of  Magnesium           .            .            .                        .  286 
Common  Salts  of  Magnesium           ....  286 
Electrolysis  of  Magnesium  Solutions     ....  287 

32.  Deposition  of  Cerium.  Lanthanium,  and  Didymium  .  288 

33.  Deposition  of  Gallium    ......  288 

34.  Deposition  of  Aluminium      .....  289 
Electrolysis  of  Salts  of  Aluminium         ....  289 

35.  Deposition  of  Glucinium       .....  292 

36.  Deposition  of  Calcium                .....  292 
Common  Salts  of  Calcium    .....  292 
Electrolysis  of  Salts  of  Calcium              ....  293 

37.  Deposition  of  Strontium        .....  294 
Electrolysis  of  Salts  of  Strontium           ....  294 

38.  Deposition  of  Barium             .....  295 
Electrolysis  of  Salts  of  Barium  .....  295 


CLASS  VI.    Alkali  Metals. 

• 

39.  Deposition  of  Lithium    ......  29=5 

Electrolysis  of  Salts  of  Lithium        ....  296 

40.  Deposition  of  Sodium     ......  297 

Ordinary  Salts  of  Sodium      .....  297 

Electrolysis  of  Salts  of  Sodium  .....  297 

41.  Deposition  of  Potassium       .....  298 
Ordinary  Salts  of  Potassium       .....  298 
Electrolysis  of  Salts  of  Potassium     ....  299 
Electrolysis  of  Fused  Potassic  Fluoride             .            .            .  301 

42.  Deposition  of  Rubidium  and  Caesium  .  .  .  305 

43.  >,           M      Ammonium          .....  305 
Electrolysis  of  Salts  of  Ammonium  ....  305 


Contents.  xix 

Deposition  of  Individual  Substances — continued. 

CLASS  VII.    Metalloids. 

PAGE 

44.  Deposition  of  Titanium  ......     307 

45.  ,  Silicon  .....          308 

Boron       ......     308 

Carbon  .....  309 

Phosphorus          .....     310 


46. 

47- 
48. 


49.  ,             Selenium         .....  310 

50.  ,             Sulphur    ......  310 

51.  ,  Iodine  ....  .311 

52.  ,  Bromine  .  .  ,  .  .  .311 

53.  ,    "         Chlorine          .  .  .  .  .311 

54.  ,             Fluorine                ,            .            ,.                         .  311 
55-              ,             Oxygen            .....  312 
56.             ,             Nitrogen  ......  312 

SECTION  B. 
SPECIAL  TECHNICAL  SECTION. 

General  Workshop  Arrangements    .  313 

Vats  for  Solutions           .......  315 

Cleaning  Articles  for  receiving  a  deposit      ....  315 

'  Stopping  off'  to  prevent  Deposition     .....  323 

'  Quicking '  the  surfaces  of  Articles  .....  323 

'Wireing'  Articles          .......  325 

Voltaic  Batteries        .            .            .            .            .            .            .  326 

Wollaston's             .......  326 

Smee's    ........  327 

Daniell's       ........  327 

Bunsen's.            .......  328 

Grove's         ........  329 

Relative  strength  of  different  Batteries         ....  329 

„       advantages        ,,                ,,                    .            .            .            .  329 

Liquids  for  Exciting  Batteries           .....  330 

Amalgamating  zinc  plates  and  rods        .....  332 

Selection  of  Zinc  for  Batteries           .....  333 

Outer  Cells  for  Batteries             ......  334 

Selection  of  Porous  Cells  for  Batteries          ....  334 

Screws  for  Binding  and  connecting  Wires,  &c.              .            .            .  334 

Management  of  Batteries      ......  335 

Regulation  of  Electric-power      ......  337 

Selection  of  Depositing  Processes    .  339 

'  Pyro-plating '    .            .            .            .            .            .                         .  339 

Selection  of  Depositing  Liquids       .            .            •           «           .  340 


xx  Contents. 


PAGE 

Testing  a  Depositing  Liquid      ......  341 

Practical  Arrangement  of  Depositing  Solutions       .  .  .  341 

Proper  positions  of  Articles  and  Dissolving  Plates  in  the  Vats .  .  343 

Regulation  of  Deposit  ..  _.  .  .  .  .  344 

Magneto-electric  Machines        ..  ..  .  .  .  .  347 

Thermo-electric  Piles  ........  351 

SPECIAL   INFORMATION   RESPECTING  SUBSTANCES,    ETC.,    USED  IN 
THE  ART. 

Water,  Acids,  Salts,  Alkalies,  Blacklead,  &c.           .            .            .  354 

Preparation  of  Caustic-potash   .             .....  360 

Making  Cyanide  of  Potassium         \  .  .  .  .361 

Testing        „                    ,,                      -.                                                  .  363 

Poisons  and  their  Antidotes,  &c.      .            .            .            .            .  365 

List  of  Books  on  Electro-deposition     .            .            .            .            .  369 

Patents          ,,                                  .            .            .            .  37* 

Tables  of  Useful  Numerical  Data        .....  385 

Nomenclature  of  Electrical  Units  .....  387 

INDEX  ....  -389 


THE 

ART  OF  ELECTRO-METALLURGY. 

HISTORICAL  SKETCH  OF  ELECTRO-METALLURGY. 

THE  earliest  known  facts  respecting  the  electro-deposition 
of  metals  were  those  in  which  one  metal,  by  being  dipped 
into  a  solution  of  another,  became  coated  with  the  latter 
metal.  For  instance,  iron  or  steel,  when  dipped  into  a  solu- 
tion of  blue  vitriol,  became  covered  with  a  coating  of  copper ; 
copper,  dipped  into  a  solution  of  mercury,  became  amalga- 
mated ;  zinc,  immersed  in  a  solution  of  lead,  formed  a  tree 
of  lead,  and  in  one  of  silver  produced  the  arbor  Diana. 
These  and  other  similar  facts  of  a  chemical  nature  were 
known  long  before  the  discovery  of  voltaic  electricity. 
Gilding  and  silvering  on  metals  had  been  known  for  many 
ages  ;  gilded  statues  and  bronzes  have  been  found  in  the 
tombs  of  the  ancient  Egyptians.  Both  Pliny  and  Vitruvius 
speak  of  processes  of  gilding  and  silvering  ;  but  these  early 
processes  appear  to  have  been  effected  by  means  of  amal- 
gams of  mercury,  and  not  by  electro-chemical  methods. 
Zosimus,  however,  speaks  of  the  deposition  of  bright  metal- 
lic copper  from  its  solution  by  means  of  iron.  Paracelsus 
also  and  Bernard  de  Palissy,  a  thousand  years  later,  were 
acquainted  with,  and  describe,  the  means  of  coating  copper 

B 


2  The  A  rt  of  Electro-Metallurgy. 

and  -iron  with  silver  by  simple  immersion  in  a  solution  of 
silver. 

One  of  the  earliest  recorded  facts  in  connection  with 
voltaic  electrolysis  is  that  observed  by  Sulzer,  who  in  the 
year  1752  remarked  :  'If  you  join  two  pieces  of  lead  and 
silver,  so  that  they  shall  be  upon  the  same  plane,  and  then 
lay  them  npor.  i|ie  tpngue,  you  will  notice  a  certain  taste  re- 
sembling that  of  "greenvYitriol,  while  each  piece  apart  produces 
no  i'.ich  seivsation";^  Histoire  de  I'Academie  des  Sciences  et 
Belles-LettreYole'Berlm ').  The  earliest  known  fact  of  elec- 
trolysis by  separate  electric  discharge  appears  to  be  that  of 
Paetz  and  Van  Troostwik,  who  in  the  year  1790  decom- 
posed water  into  its  two  constituent  gases,  bypassing  electric 
sparks  through  it  by  means  of  very  fine  gold  wires  (De  la 
Rive's  'Treatise  on  Electricity/  vol.  ii.,  p.  443). 

But  all  these  were  empirical,  stagnant,  and  comparatively 
unfruitful  facts ;  no  great  progress  resulted  from  them  because 
they  were  not  generalised  upon,  and  were  not  recognised  as 
instances  of  any  great  law  or  principle.  Electrolysis  did  not 
start  into  active  and  real  progress  until  after  Volta  made  his 
great  discovery  of  chemical  electricity  in  the  year  1799.  About 
that  time  he  produced  his  crown  of  cups,  which  was  the 
first  arrangement  by  means  of  which  a  current  of  voltaic 
electricity  could  be  produced  for  any  continued  length  of  time. 

Cruickshank  soon  afterwards  devised  his  well-known 
trough  battery,  in  which  zinc  and  copper  plates  were  fixed 
in  vertical  grooves,  so  as  to  form  a  more  powerful  and  com- 
pact arrangement  (Highton's  '  Electric  Telegraph/ pp.  13,  14, 
and  29). 

Nicholson  and  Carlisle,  on  May  2, 1800,  first  decomposed 
water  by  means  of  a  voltaic  current  (Highton's  '  Electric  Te- 
legraph/ pp.  27  and  29). 

Dr.  Henry,  of  Manchester,  also  about  the  same  year,  de- 
composed nitric  and  sulphuric  acids,  and  resolved  ammonia 
into  its  constituent  gases  by  similar  means  ('  Encyclopedia 
Metropolitan/  vol.  iv.,  pp.  221  and  611). 


Early  Facts  of  Electrolysis.  3 

In  the  year  1801  Wollaston  remarked  that  'if  a  piece  of 
silver,  in  connection  with  a  more  positive  metal,  be  put  into 
a  solution  of  copper,  the  silver  is  coated  over  with  copper, 
which  coating  will  stand  the  operation  of  burnishing'  ('  Philo- 
sophical Transactions  of  the  Royal  Society,'  1801). 

In  the  same  year  Gerboin  first  noticed  the  movements 
of  mercury  in  a  conducting  liquid  when  a  voltaic  current  was 
passed  through  the  liquid  metal ;  we  now  know  that  those 
movements  were  due  to  electrolysis  (De  la  Rive's  '  Treatise 
on  Electricity,'  vol.  ii.,  p.  433).  Hisinger  and  Berzelius  also, 
in  1803,  found  by  means  of  many  experiments  that,  under 
the  influence  of  a  voltaic  current,  the  elements  of  water  and 
of  neutral  salts  were  transferred  to  the  respective  poles  of  the 
battery  ('  Encyclopedia  Metropolitan^'  vol.  iv.,  pp.  221,  222). 
About  the  same  time  Cruickshank  passed  a  voltaic  current, 
by  means  of  silver  wires,  through  solutions  of  acetate  of  lead, 
sulphate  of  copper,  nitrate  of  silver,  and  several  other  salts, 
and  found  that  the  metals  attached,  themselves  to  the  wire 
connected  with  the  zinc-end  of  the  battery ;  and  stated  that 
the  metals  were  '  revived '  so  completely  as  to  suggest  to  hirn 
the  analysis  of  minerals  by  means  of  the  voltaic  current 
(Wilkinson's  'Elements  of  Galvanism/  vol.  ii.,  1804,  p.  54). 

The  first  result  of  a  decidedly  practical  form  in  electro- 
gilding  was  that  of  Brugnatelli,  who,  in  the  year  1805,  gilded 
two  silver  medals  by  making  them  the  negative  pole  in  a 
newly-made  and  well-saturated  solution  of  ammoniuret  of 
gold  (' Philosophical  Magazine,'  1805).  He  also  electro- 
deposited  bright  metallic  silver  upon  platinum,  and  ob- 
served that  when  the  current  entered  the  liquid  by  means 
of  a  pole  of  copper  or  zinc,  those  metals  were  dissolved 
and  then  deposited  upon  the  negative  pole  (see  his '  Annals 
of  Chemistry').  One  of  the  greatest  discoveries  in  the 
subject,  however,  was  that  of  Sir  Humphry  Davy,  made  on 
October  6,  1807.  He  passed  a  powerful  electric  cur- 
rent, from  a  battery  composed  of  274  cells,  through  a  frag- 
ment of  moistened  potash,  and  deposited  the  metal  potassium 

B  2 


4  The  A  rt  of  Electro-Metallurgy. 

itself  upon  the  negative  platinum  wire.  Seebeck,  of  Berlin,  in 
the  year  1822  discovered  thermo-electricity  by  observing  that, 
when  the  soldered  junction  of  two  different  metals  (bismuth 
and  copper)  was  heated,  an  electric  current  was  produced. 
In  1824  Sir  H.  Davy  attempted  to  protect  the  copper  sheath- 
ing of  ships  by  means  of  strips  of  zinc  attached  to  it.  Nobili, 
in  the  year  1826,  discovered  that  when  a  current  of  voltaic 
electricity  was  passed  into  a  solution  of  acetate  of  lead  by 
means  of  a  plate  of  platinum,  and  out  of  it  by  means  of  a  pla- 
tinum wire,  rings  of  beautiful  colours,  caused  by  the  forma- 
tion of  thin  films  of  peroxide  of  lead,  appeared  on  the 
platinum  plate  •  this  effect  was  named  '  metallo-chromy.' 

Magneto-electricity  was  discovered  by  Faraday.  In  the 
year  1831  he  produced  a  spark  by  pulling  a  keeper  (covered 
with  a  coil  of  insulated  wire)  from  the  poles  of  a  magnet ;  he 
also  obtained  a  magneto  electric  current  by  rotating  a  copper 
plate  between  the  poles  of  a  magnet,  and  by  sliding  a  coil  of 
insulated  copper  wire  upon  a  steel -bar  magnet.  In  1834  he 
made  the  important  discovery,  that  when  a  voltaic  carrent 
was  passed  through  different  salts  in  solution  or  in  a  state  of 
fusion,  the  amount  of  salt  decomposed  by  the  current  was  in 
direct  proportion  to  the  quantity  of  electricity  ;  and  that  the 
quantities  of  substances  dissolved  and  set  free  in  electrolysis 
were  in  definite  proportions  by  weight,  and  that  those  pro- 
portions were  identical  with  the  ordinary  chemical  equiva- 
lents of  the  substances,  and  thus  established  the  important 
law  of  definite  electro-chemical  action.  He  also  proved  that 
the  quantity  of  electricity  from  a  voltaic  battery  depends 
upon  the  size  of  the  immersed  portion  cf  the  plates,  and  that 
the  intensity  of  the  current  depends  upon  the  number  of  al- 
ternate pairs  of  metals ;  and  used  a  voltameter  to  ascertain 
the  strength  of  the  current. 

In  1836  Mr.  De  la  Rue  devised  a  peculiar  form  of 
DanielFs  battery,  and  observed  that  *  the  copper  plate  is  also 
covered  with  a  coating  of  metallic  copper,  which  is  continu- 
ally being  deposited ;  an  d  so  perfect  is  the  sheet  of  copper 


Jordan's  Experiments.  5 

thus  formed  that,  being  stripped  off,  it  has  the  counterpart 
of  every  scratch  of  the  plate  on  which  it  is  deposited ' 
('Philosophical  Magazine,'  1836). 

In  1837  Dr.  Golding  Bird  decomposed,  by  means  of  a 
voltaic  current,  solutions  of  the  chlorides  of  sodium,  potas- 
sium, and  ammonium,  and  deposited  their  respective  metals 
on  a  negative  pole  of  mercury,  and  thus  obtained  their  amal- 
gams ('  Philosophical  Transactions  of  the  Royal  Society/  1 83  7, 

P-  37)- 

Several  persons  now  made  experiments  upon  the  electro- 
deposition  of  metals  at  about  the  same  time,  and  brought 
electro-metallurgy  into  prominent  notice.  Professor  Jacobi, 
of  St.  Petersburg,  published  his  galvano-plastic  process,  '  a 
method  of  converting  any  line,  however  fine,  engraved  on 
copper,  into  a  relief  by  galvanic  process,  applicable  to  cop- 
per-plate engravings,  medals,  stereotype  plates,  ornaments, 
and  to  making  calico-printing  blocks  and  patterns  for  paper- 
hangings '  ('Athenaeum,'  May  4,  1839).  Mr.  T.  Spencer,  of 
Liverpool,  also  on  May  8,  1839,  gave  notice  to  read  a  paper 
on  the  '  Electrotype  Process '  to  the  Liverpool  Polytechnic 
Society,  but  the  paper  was  not  read  until  September  13  in  the 
same  year. 

Meanwhile,  Mr.  C.  J.  Jordan,  on  May  22,  1839,  sent  a 
letter  to  the  '  London  Mechanics'  Magazine,'  which  was  pub- 
lished on  June  8,  1839.  After  stating  that  his  experiments 
were  made  '  about  the  commencement  of  last  summer,  with 
a  view  of  obtaining  impressions  from  engraved  copper 
plates/  it  proceeds  as  follows  : 

'  It  is  well  known  to  experimentalists  on  the  chemical 
action  of  voltaic  electricity  that  solutions  of  several  metallic 
salts  are  decomposed  by  its  agency,  and  the  metal  procured 
in  a  free  state.  Such  results  are  very  conspicuous  with  cop- 
per salts,  which  metal  may  be  obtained  from  its  sulphate 
(blue  vitriol)  by  simply  immersing  the  poles  of  a  galvanic 
battery  in  its  solution,  the  positive  wire  becoming  gradually 
coated  with  copper.  This  phenomenon  of  metallic  reduction 


6  The  Art  of  Electro-Metallurgy. 

is  an  essential  feature  in  the  action  of  sustaining  batteries, 
the  effect,  in  this  case,  taking  place  on  more  extensive  sur- 
faces. But  the  form  of  voltaic  apparatus  which  exhibits  this 
result  in  the  most  interesting  manner,  and  relates  more  im- 
mediately to  the  subject  of  the  present  communication,  may 
be  thus  described  :  It  consists  of  a  glass  tube,  closed  at  one 
extremity  with  a  plug  of  plaster-of- Paris,  and  nearly  filled 
with  a  solution  of  sulphate  of  copper  ;  this  tube  and  its  con- 
tents are  immersed  in  a  solution  of  common  salt.  A  plate 
of  copper  is  placed  in  the  first  solution,  and  is  connected  by 
means  of  a  wire  and  solder  with  a  zinc  plate,  which  dips 
into  the  latter.  A  slow  electric  action  is  thus  established 
through  the  pores  of  the  plaster,  which  it  is  not  necessary  to 
mention  here ;  the  result  of  which  is  the  precipitation  of 
minutely  crystallised  copper  on  the  plate  of  that  metal,  in  a 
state  of  greater  or  less  malleability,  according  to  the  slowness 
or  rapidity  with  which  it  is  deposited.  In  some  experiments 
of  this  nature,  on  removing  the  copper  thus  formed  I  re- 
marked that  the  surface  in  contact  with  the  plate  equalled 
the  latter  in  smoothness  and  polish,  and  mentioned  this  fact 
to  some  individuals  of  my  acquaintance.  It  occurred  to  me, 
therefore,  that  if  the  surface  of  the  plate  was  engraved  an 
impression  might  be  obtained.  This  was  found  to  be  the 
case,  for,  on  detaching  the  precipitated  metal,  the  most  deli- 
cate and  superficial  marking,  from  the  fine  particles  of  pow- 
der used  in  polishing  to  the  deeper  touches  of  a  needle  or 
graver,  exhibited  their  corresponding  impressions  in  relief 
with  great  fidelity.  It  is,  therefore,  evident  that  this  princi- 
ple will  admit  of  improvement,  and  that  casts  and  moulds 
may  be  obtained  from  any  form  of  copper. 

'  This  rendered  it  probable  that  impressions  may  be  ob- 
tained from  those  other  metals  having  an  electro-negative 
relation  to  the  zinc  plate  of  the  battery.  With  this  view, 
a  common  printing  type  was  substituted  for  the  copper-plate, 
and  treated  in  the  same  manner.  This  also  was  successful  ; 
the  reduced  copper  coated  that  portion  of  the  type  immersed 


Spencer  s  Experiments.  7 

in  the  solution.  This,  when  removed,  was  found  to  be  a 
perfect  matrix,  and  might  be  employed  for  the  purpose  of 
casting  when  time  is  not  an  object. 

1  It  appears,  therefore,  that  this  discovery  may  be  turned 
to  practical  account.  It  may  be  taken  advantage  of  in  pro- 
curing casts  from  various  metals,  as  above  alluded  to  ;  for 
instance,  a  copper  die  may  be  formed  from  a  cast  of  a  coin 
or  medal,  in  silver,  type  metal,  or  lead,  &c.,  which  may  be 
employed  for  striking  impressions  in  soft  metals.  Casts 
may  probably  be  obtained  from  a  plaster  surface  surrounding 
a  plate  of  copper ;  tubes  or  any  small  vessel  may  also  be 
made  by  precipitating  the  metal  around  a  wire,  or  any  kind 
of  surface,  to  form  the  interior,  which  may  be  removed  me- 
chanically, by  the  aid  of  an  acid  solvent,  or  by  heat. 

*  C.  J.  JORDAN. 

'May  22,  1839.' 

Mr.  Spencer  in  his  paper,  after  making  some  preliminary 
remarks,  states  : — 'In  the  latter  part  of  September  1837  I 
was  induced  to  make  some  electro-chemical  experiments 
with  single  pairs  of  plates,  consisting  of  small  pieces  of  zinc 
and  equal-sized  pieces  of  copper,  connected  together  with 
wires  of  the  latter  metal.  It  was  intended  that  the  action 
should  be  slow  ;  the  fluids  in  which  the  metallic  electrodes 
were  immersed  were  in  consequence  separated  by  thin  discs 
of  plaster-of-Paris.  In  one  cell  thus  formed  was  placed 
sulphate  of  copper  in  solution,  in  the  other  a  weak  solution 
of  common  salt.  I  need  scarcely  add  that  the  copper 
electrode  was  placed  in  the  cupreous  solution,  the  other 
being  in  that  of  the  salt.  I  mention  these  experiments 
briefly ;  not  because  they  are  directly  connected  with  what 
I  shall  have  to  lay  before  the  Society,  but  because,  by  a 
portion  of  their  results,  I  was  induced  to  come  to  the  con- 
clusions I  have  done  in  the  following  paper.  I  was  desirous 
that  no  action  should  take  place  on  the  wires  by  which  the 
electrodes  were  held  together;  and  to  obtain  this  object  I 


8  The  A  rt  of  Electro-Metallurgy. 

varnished  them  with  sealing-wax  varnish,  but  in  one  instance 
I  dropped  a  portion  on  the  copper  electrode  that  was 
attached.  I  thought  nothing  of  this  circumstance  at  the 
moment,  but  put  the  experiment  inaction. 

'  This  operation  was  conducted  in  a  glass  vessel ;  I  had 
consequently  an  opportunity  of  occasionally  examining  its 
progress  from  the  exterior.  After  the  lapse  of  a  few  days, 
metallic  crystals  had  covered  the  copper  electrode — with  the 
exception  of  that  portion  which  had  been  spotted  with  the 
drops  of  varnish.  I  at  once  saw  that  I  had  it  in  my  power 
to  guide  the  metallic  deposition  in  any  shape  or  form  I  chose, 
by  a  corresponding  application  of  varnish  or  other  non- 
metallic  substance. 

*  I  had  been  aware  of  what  everyone  who  uses  a  sustain- 
ing galvanic  battery  with  sulphate  of  copper  must  know,  that 
the  copper  plates  acquire  a  coating  of  copper  from  the  action 
of  the  battery  ;  but  I  had  never  thought  of  applying  it  to  a 
useful  purpose,  except  to  multiply  the  plates  of  a  species  of 
battery,  which  I  did  in  1836.  My  present  attempt  was  with 
a  piece  of  thin  copper  plate  having  about  four  inches  of 
superficies,  with  an  equal-sized  piece  of  zinc,  connected  as 
before  by  a  piece  of  copper  wire.  I  gave  the  copper  a  coat- 
ing of  soft  cement,  consisting  of  bees'- wax,  rosin,  and  a  red 
earth.  It  was  compounded  in  the  way  recommended  by 
Dr.  Faraday,  in  his  work  on  Chemical  Manipulation,  but 
with  a  larger  proportion  of  wax.  The  plate  received  its 
coating  while  hot.  When  it  was  cold,  I  scratched  the  initials 
of  my  name  rudely  on  the  plate,  taking  special  care  that  the 
cement  was  quite  removed  from  the  scratches,  that  the 
copper  might  be  thoroughly  exposed.  This  was  put  in  action 
in  a  cylindrical  glass  vessel,  about  half  filled  with  a  saturated 
solution  of  sulphate  of  copper.  I  then  took  a  common  gas 
glass,  similar  to  that  used  to  envelope  an  argand  burner,  and 
filled  one  end  of  it  with  plaster-of-Paris  acting  as  a  partition 
to  separate  the  fluids,  but  at  the  same  time  being  sufficiently 


Spencer's  Experiments.  9 

porous  to  allow  the  electro-chemical  action  to  permeate  its 
substance. 

1 1  now  bent  the  wire  in  such  a  manner  that  the  zinc  end 
of  the  arrangement  should  be  in  the  saline  solution,  while 
the  copper  end,  when  in  its  place,  should  be  in  the  cupreous 
solution.  The  gas  glass,  with  the  wire,  was  then  placed  in 
the  vessel  containing  the  sulphate  of  copper. 

'  It  was  then  suffered  to  remain  at  rest,  when  in  a  few 
hours  I  perceived  that  action  had  commenced,  and  that  the 
portion  of  the  copper  rendered  bare  by  the  scratches  had 
become  gradually  coated  with  pure,  bright  deposited  metal, 
whilst  all  the  surrounding  portions  were  not  at  all  acted  on, 
I  now  saw  my  former  observations  realised  ;  but  whether 
the  deposition  so  formed  would  retain  its  hold  on  the  plate, 
and  whether  it  would  be  of  sufficient  solidity  or  strength  to 
bear  the  working  if  applied  to  a  useful  purpose,  became 
questions  which  I  now  determined  to  solve  by  experiment. 
It  also  became  a  question,  should  I  be  successful  in  these 
two  points,  whether  I  should  be  able  to  produce  lines  suffi- 
ciently in  relief  to  print  from.  This  latter  appeared  to 
depend  entirely  on  the  nature  of  the  cement  or  etching- 
ground  I  might  use. 

'  This  I  endeavoured  to  solve  at  once  ;  and,  I  may  state, 
it  appeared  at  the  time  to  be  the  main  difficulty,  as  my  im- 
pression then  was,  that  little  less  than  one-eighth  of  an  inch 
would  be  requisite  to  print  from. 

*  I  now  procured  a  piece  of  copper,  and  gave  it  a  coating 
of  a  modification  of  the  cement  I  have  already  mentioned, 
and,  having  covered  it  to  about  one-eighth  of  an  inch  in 
thickness,  I  took  a  steel  print  and  endeavoured  to  draw  lines 
in  the  form  of  network,  that  should  entirely  penetrate  the 
cement,  and  leave  the  surface  of  the  copper  exposed.  But 
in  this  I  experienced  much  difficulty  from  the  thickness  I 
deemed  it  necessary  to  use,  more  especially  when  I  came  to 
draw  the  cross  lines  of  the  network.  The  cement  being 
soft,  the  lines  were  pushed,  as  it  were,  into  each  other,  and 


I  o  The  A  rt  of  Electro-Metallurgy. 

when  it  was  made  of  harder  texture,  the  intervening  squares 
of  the  network  chipped  off  the  surface  of  the  metallic  plate. 
However,  those  that  remained  perfect  I  put  in  action  as 
before. 

'  In  the  progress  of  this  experiment  I  discovered  that  the 
solidity  of  the  metallic  deposition  depended  entirely  on  the 
weakness  or  intensity  of  the  electro-chemical  action,  which  I 
knew  I  had  in  my  power  to  regulate  at  pleasure,  by  the 
thickness  of  the  intervening  wall  of  plaster- of- Paris,  and  by 
the  coarseness  or  fineness  of  the  material.  I  made  three 
similar  experiments,  altering  the  texture  and  thickness  of  the 
plaster  each  time,  by  which  I  ascertained  that  if  the  parti- 
tions were  thin  and  coarse,  the  metallic  depositions  proceeded 
with  great  rapidity,  but  the  crystals  were  pliable  and  easily 
separated  ;  on  the  other  hand,  if  I  made  them  thicker,  and 
of  a  little  finer  material,  the  action  was  slower,  but  the  me- 
tallic deposition  was  as  solid  and  ductile  as  copper  formed 
by  the  usual  methods  ;  indeed,  when  the  action  was  exceed- 
ingly slow,  I  have  had  a  metallic  deposition  apparently 
much  harder  than  common  sheet-copper,  but  more  brittle. 

'  There  was  one  most  important,  and  to  me  discouraging, 
circumstance  attending  these  experiments,  which  was,  that 
when  I  heated  the  plates  to  get  off  the  covering  of  cement, 
the  meshes  of  copper  network  occasionally  came  off  with 
it.  I  at  one  time  imagined  this  difficulty  insuperable,  as 
it  appeared  that  I  had  cleared  the  cement  entirely  from 
the  surface  of  the  copper  that  I  meant  to  have  exposed;  and 
I  concluded  that  there  must  be  differences  in  the  molecular 
arrangement  of  copper  prepared  by  heat  and  that  prepared 
by  voltaic  action  which  prevented  their  chemical  combina- 
tion. However,  I  determined,  should  this  prove  so,  to 
turn  it  to  account  in  another  manner,  which  I  shall 
relate  in  the  second  portion  of  the  paper. 

'  I  now  occupied  myself  for  a  considerable  period  in 
making  experiments  on  this  latter  section  of  the  subject. 

'In  one  of  them  I  found,  on  examination,  that  a  portion 


Spencer's  Experiments.  1 1 

of  the  copper  deposition,  which  I  had  been  forming  on  the 
surface  of  a  coin,  adhered  so  strongly  that  I  was  quite 
unable  to  get  it  off;  indeed,  a  chemical  combination  had 
apparently  taken  place.  This  was  only  on  one  or  two  spots 
on  the  prominent  parts  of  the  coin.  I  immediately  recol- 
lected that  on  the  day  I  put  the  experiment  in  action  I  had 
been  using  nitric  acid  for  another  purpose  on  the  table  I 
was  operating  on,  and  that  in  all  probability  the  coin  might 
have  been  laid  down  where  a  few  drops  of  the  acid  had  acci- 
dentally fallen.  Bearing  this  in  view,  I  took  a  piece  of  cop- 
per, coated  it  with  cement,  made  a  few  scratches  on  its  surface 
until  the  copper  appeared,  and  immersed  it  for  a  short  time 
in  dilute  nitric  acid,  until  I  perceived,  by  an  elimination  of 
nitrous  gas,  that  the  exposed  portions  were  acted  upon 
sufficiently  to  be  slightly  corroded.  I  washed  the  copper  in 
water,  and  put  it  in  action  as  before  described.  In  forty- 
eight  hours  I  examined  it,  and  found  the  lines  were  entirely 
filled  with  copper.  I  applied  heat,  and  then  spirits  of  tur- 
pentine, to  get  off  the  cement,  and,  to  my  satisfaction,  I 
found  that  the  voltaic  copper  had  completely  combined  it- 
self with  the  sheet  in  which  it  was  deposited. 

' 1  then  gave  a  plate  a  coating  of  cement  to  a  considerable 
thickness,  and  sent  it  to  an  engraver;  but  when  it  was 
returned  I  found  the  lines  cleared  out  so  as  to  be  wedge- 
shaped,  or  somewhat  in  the  form  of  a  V,  leaving  a  hair-line  of 
the  copper  exposed  at  the  bottom,  and  a  broad  space  near 
the  surface ;  and  where  the  turn  of  the  letters  took  place  the 
top  edges  of  the  lines  were  galled  and  rendered  rugged  by 
the  action  of  the  graver.  This,  of  course,  was  an  important 
objection,  which  I  have  since  been  able  to  remedy  in  some 
degree  by  an  alteration  in  the  shape  of  the  graver,  which 
should  be  made  of  a  shape  more  resembling  a  narrow  paral- 
lelogram than  those  in  common  use :  some  engravers  have 
many  of  their  tools  so  made.  I  did  not  put  this  plate  in 
action,  as  I  saw  that  the  lines,  when  in  relief,  would  have 
been  broad  at  the  top  and  narrow  at  the  bottom.  I  took 


1 2  The  A  rt  of  Electro- Metallurgy. 

another  plate,  gave  it  a  coating  of  the  wax,  and  had  it  writ- 
ten on  with  a  mere  point.  I  deposited  copper  on  the  lines, 
and  afterwards  had  it  printed  from.* 

'  I  now  considered  part  of  the  difficulty  removed  :  the 
principal  one  yet  remaining  was  to  find  a  cement,  or  etching- 
ground,  the  texture  of  which  should  be  capable  of  being  cut 
to  the  required  depth,  without  raising  what  is  technically 
called  a  burr,  and  at  the  same  time  of  sufficient  toughness 
to  adhere  to  the  plate  when  reduced  to  a  small,  isolated 
point,  which  would  necessarily  occur  in  the  operation  which 
wood-engravers  term  cross-hatching. 

'  I  have  since  learned  from  practical  engravers  that  much 
less  relief  is  necessary  to  print  from  than  I  had  deemed 
indispensable,  and  that,  on  becoming  more  familiar  with  the 
cutting  of  the  wax-cement,  they  would  be  enable'd  to  engrave 
in  it  with  facility  and  precision. 

'  I  tried  a  number  of  experiments  with  different  combina- 
tions of  wax,  resins,  varnishes,  earths,  and  metallic  oxides, 
all  with  more  or  less  success.  One  combination  that  ex- 
ceeded all  others  in  its  texture  was  principally  composed  of 
bees'-wax,  resin,  and  white-lead.  This  had  nearly  every 
requisite,  so  that  I  was  enabled  to  polish  the  surface  of  the 
plate  with  it  until  it  was  nearly  as  smooth  as  a  plate  of  glass. 
With  this  compound  I  had  two  plates,  five  inches  by  seven, 
coated  over,  and  portions  of  maps  cut  on  the  cement,  which 
I  had  intended  should  have  been  printed  off.  I  applied 
the  same  process  to  these  as  to  the  others,  immersing  them 
into  dilute  nitric  acid  before  putting  them  in  action — indeed 
I  suffered  them  to  remain  about  ten  minutes  in  the  solution. 
I  then  put  them  into  the  voltaic  arrangement.  The  action 
proceeded  slowly  and  perfectly  for  a  few  days,  when  I  re- 
moved them.  I  applied  heat,  as  usual,  to  remove  the  cement, 
but  all  came  away,  as  in  a  former  instance— the  voltaic 
copper  peeling  off  the  plate  with  the  greatest  facility.  I 

*  This  plate  was  shown  to  friends,  and  also  specimens  of  printing 
from  it,  in  1838. 


Spencer's  Experiments  13 

was  much  puzzled  at  this  unexpected  result,  but,  on  cleaning 
the  plate,  I  discovered  a  delicate  trace  of  lead^  exactly  cor- 
responding to  the  lines  drawn  on  the  cement  previous  to  the 
immersion  in  the  dilute  acid.  The  cause  of  this  failure  was 
at  once  obvious  :  the  carbonate  of  lead  I  had  used  to  com- 
pound the  etching- ground  had  been  decomposed  by  the 
dilute  nitric  acid,  and  the  metallic  lead  thus  reduced  had 
deposited  itself  on  the  exposed  portions  of  the  copper  plates, 
preventing  the  voltaic  copper  from  chemically  combining 
with  the  sheet  of  copper.  I  was  now  with  regret  obliged  to 
give  up  this  compound  and  to  adopt  another,  consisting  of 
bees'-wax,  common  resin,  and  a  small  portion  of  plaster-of- 
Paris.  This  seems  to  answer  the  purpose  tolerably,  though 
I  have  no  doubt,  by  an  extended  practice,  a  better  may  still 
be  obtained  by  a  person  practically  acquainted  with  the 
etching-grounds  in  use  among  engravers. 

'  I  now  proceed  to  the  second,  and,  I  believe,  the  most 
satisfactory  portion  of  the  subject.  Although  I  have  placed 
these  experiments  last,  some  of  them  were  made  at  the 
same  time  with  the  others  already  described,  and  some  of 
them  before  ;  but  to  render  the  subject  more  intelligible  I 
have  placed  them  thus. 

*  The  members  of  the  Society  will  recollect  that,  on  the 
first  evening  it  met,  I  read  a  paper  on  the  "  Production  of 
Metallic  Veins  in  the  Crust  of  the  Earth,"  and  that,  among 
other  specimens  of  cupreous  crystallization  which  I  produced 
on  that  occasion,  I  exhibited  two  coins, — one  wholly  covered 
with  metallic  crystals,  the  other  on  one  side  only.  It  was 
used  under  the  following  circumstances  :  when  about  to 
make  the  experiment,  I  had  not  a  slip  of  copper  at  hand  to 
form  the  negative  end  of  my  arrangement,  and,  as  a  good 
substitute,  I  took  a  penny  and  fastened  it  to  one  end  of  the 
wire  and  put  it,  in  connection  with  a  piece  of  zinc,  in  the 
apparatus  already  described. 

Voltaic  action  took  place,  and  the  copper  coin  became 
covered  with  a  deposition  of  copper  in  a  crystalline  form. 


14  The  Art  of  Electro- Metallurgy. 

But  when  about  to  make  another  experiment,  and  being  de- 
sirous of  using  the  piece  of  wire  used  in  the  first  instance, 
I  pulled  it  off  the  coin  to  which  it  was  attached.  In  doing 
this,  a  piece  of  the  deposited  copper  came  off  with  it ;  on 
examining  the  under  portion  of  which,  I  found  it  contained 
an  exact  mould  of  a  part  of  the  head  and  letters  of  the  coin, 
as  smooth  and  sharp  in  every  respect  as  the  original  on 
which  it  was  deposited.  I  was  much  struck  with  this  at  the 
time,  but,  on  examination,  the  deposited  metal  was  very 
brittle.  This,  and  the  fact  that  it  would  require  a  metallic 
nucleus  to  aggregate  on,  made  me  apprehensive  that  its 
future  usefulness  would  be  materially  abridged ;  but  it  was 
reserved  for  future  experiment,  and  in  consequence  laid  aside 
for  a  time,  until  my  attention  was  recalled  to  the  subject  in 
a  subsequent  experiment,  already  detailed,  by  the  drops  of 
varnish  on  a  slip  of  copper.  Finding  in  this  instance  that 
the  deposit  would  take  the  direction  of  any  non-conducting 
material,  and  be,  as  it  were,  guided  by  it,  I  was  induced  to 
give  the  previous  branch  of  the  subject  a  second  trial,  be- 
cause I  had,  in  the  first  instance,  supposed  that  the  deposi- 
tion would  only  take  place  continuously,  and  not  as  isolated 
specks  of  a  metallic  surface,  as  I  now  found  it  would  ;  but 
the  principal  inducement  to  investigate  the  subject  was  the 
fact  of  finding  that  the  deposited  copper  had  much  more 
tenacity  than  I  at  first  imagined. 

'Being  aware  of  the  apparent  natural  law  which  limits 
metallic  deposition  by  voltaic  electricity,  excepting  in  the 
presence  of  a  metallic  body,  I  perceived  that  the  uses  of  the 
process  would  in  consequence  be  extremely  limited,  except 
in  the  multiplication  of  already-engraved  plates,  as,  what- 
ever ornament  it  might  produce,  it  would  only  be  done  by 
adhering  to  the  condition  of  a  metallic  mould. 

'I  accordingly  determined  to  make  an  experiment  on  a 
very  prominent  copper  medal.  It  was  placed  in  a  voltaic 
circuit,  as  already  described,  and  deposited  a  surface  of 
copper  on  one  of  its  sides,  to  about  the  thickness  of  a  shilling. 


Spencer's  Experiments.  1 5 

I  then  proceeded  to  get  the  deposition  off.  In  this  I  expe- 
rienced some  difficulty,  but  ultimately  succeeded.  On  ex- 
amination with  a  lens,  every  line  was  as  perfect  as  the  coin 
from  which  it  was  taken.  I  was  then  induced  to  use  the 
same  piece  again,  and  let  it  remain  a  much  longer  time  in 
action,  that  I  might  have  a  thicker  and  more  substantial 
mould,  in  order  to  test  fairly  the  strength  of  the  metal.  It 
was  accordingly  put  again  in  action,  and  let  remain  until  it 
had  acquired  a  much  thicker  coating  of  the  metallic  deposi- 
tion ;  but  on  attempting  to  remove  it  from  the  medal  I 
found  I  was  unable.  It  had  apparently  completely  adhered 
to  it. 

*  I  had  often  practised  with  some  degree  of  success  a 
method  of  preventing  the  oxidation  of  polished  steel,  by 
slightly  heating  it  until  it  would  melt  fine  bees'-wax  ;  it  was 
then  wiped  apparently  completely  off,  but  the  pores  or  sur- 
face of  the  metal  became  impregnated  with  the  wax. 

1 1  thought  of  this  method,  and  applied  it  to  a  copper 
coin. 

'I  first  heated  it,  applied  wax,  and  then  wiped  it  so  com- 
pletely off,  that  the  sharpness  of  the  coin  was  not  at  all  in- 
terfered with.  I  proceeded  as  before,  and  deposited  a 
thick  coating  of  copper  on  its  surface.  Being  desirous  to 
take  it  off,  I  applied  the  heat  of  a  spirit  lamp  to  the  back, 
when  a  sharp  crackling  noise  took  place,  and  I  had  the 
satisfaction  of  perceiving  that  the  coin  was  completely 
loosened.  In  short,  I  had  a  most  complete  and  perfect 
copper  mould  of  one  side  of  a  halfpenny. 

1 1  have  since  taken  some  impressions  from  the  mould 
thus  taken,  and  by  adopting  the  above  method  with  the 
wax,  they  are  separated  with  the  greatest  ease. 

*  By  this  experiment  it  would  appear  that  the  wax  impreg- 
nates the  surface  of  the  metal  to  an  inconsiderable  depth, 
and  prevents  a  chemical  adhesion  from  taking  place  on  the 
two  surfaces ;  and  I  can  only  account  for  the  crackling  noise 
on  separation,  by  supposing  it  probable  that  the  molecular 


16  The  Art  of  Electro-Metallurgy. 

arrangement  of  the  voltaic  metal  is  different  from  that  sub- 
jected to  percussion,  and  this  difference  causes  an  unequal 
degree  of  expansibility  on  the  application  of  heat. 

'  I  now  became  of  opinion  that  this  latter  method  might 
be  applied  to  engraving  much  better  than  the  method  de- 
scribed in  the  first  portion  of  this  paper.  Having  found  in  a 
former  experiment  that  copper  in  a  voltaic  circuit  deposited 
itself  on  lead,  with  as  much  rapidity  as  on  copper,  I  took  a 
silver  coin  and  put  it  between  two  pieces  of  clean  sheet-lead, 
and  placed  them  under  a  common  screw-press.  From  the 
softness  of  the  lead,  I  had  a  complete  and  sharp  mould  of 
both  sides  of  the  coin,  without  sustaining  injury.  I  then 
took  a  piece  of  copper  wire,  soldered  the  lead  to  one  end 
and  a  piece  of  zinc  to  the  other,  and  put  them  into  the 
voltaic  arrangement  I  have  already  described.  I  did  not  in 
this  instance  wax  the  mould,  as  I  felt  assured  that  the  de- 
posited copper  would  easily  separate  from  the  lead  by  the 
application  of  heat,  from  the  different  expansibility  of  the 
two  metals. 

*  In  this  result  I  was  not  disappointed.     When  the  heat 
of  a  spirit  lamp  was  applied  for  a  few  seconds  to  the  lead 
the  copper  impression  came  easily  off.     So  complete  do  I 
think  this  latter  portion  of  the  subject,  that  I  have  no  hesita- 
tion in  asserting  that  fac-similes  of  any  coin  or  medal,  no 
matter  of  what  size,  may  be  readily  taken,  and  as  sharp  as 
the  original.     To  test  further  the  capabilities  of  this  method 
I  took  a  piece  of  lead  plate,  and  stamped  some  letters  on  its 
surface  to  a  depth  sufficient  to  print  from  when  in  relief.     I 
deposited  the  copper  on  it,  and  found  it  came  easily  off,  the 
letters  being  in  relief. 

'  Finding  from  this  experiment  that  the  extreme  softness 
of  the  lead  allowed  it  to  be  impressed  on  by  type-metal,  I 
caused  a  small  portion  of  ornamental  letter-press  to  be  set 
up  in  type,  and  placing  it  on  a  planed  piece  of  sheet-lead,  it 
ivas  subjected  to  the  action  of  a  screw-press. 

*  After  considerable  pressurej  it  was  found  that  a  perfectly 


Spencer's  Experiments.  17 

sharp  mould  of  the  whole  had  been  obtained  in  the  lead.  A 
wire  was  now  soldered  to  it,  and  it  was  placed  in  an 
apparatus  similar  in  principle,  but  larger  than  the  one  al- 
ready described.  At  the  end  of  eight  days  from  this  time 
copper  was  deposited  to  one-eighth  of  an  inch  in  thickness  ; 
it  was  subjected  to  heat,  when  the  two  metals  began  to 
loosen.  The  separation  was  completed  by  inserting  a  piece 
of  wedge-shaped  wood  between  them. 

'  I  had  now  the  satisfaction  of  perceiving  that  I  had  ob- 
tained a  most  perfect  specimen  of  stereotyping  in  copper, 
which  had  only  to  be  mounted  on  a  wooden  block  to  be 
ready  to  print  from. 

*  From  the  successful  issue  of  this  experiment,  which  was 
mainly  due  to  the  susceptibility  of  the  lead,  I  was  induced 
to  attempt  to  copy  a  wood  engraving  by  a  similar  method, 
provided  the  wood  would  bear  the  requisite  pressure.  Know- 
ing that  wood  engravings  are  executed  on  the  end  of  the 
block,  I  had  better  hopes  of  succeeding,  the  wood  being  less 
likely  to  sustain  injury. 

'  I  accordingly  procured  a  small  block,  and  placed  its 
engraved  surface  in  contact  with  a  piece  of  sheet-lead,  made 
very  clean,  and  subjected  it  to  pressure  as  in  the  former  in- 
stance. I  had  now,  as  before,  the  gratification  of  perceiving 
that  a  perfect  mould  of  the  little  block  had  been  obtained, 
and  no  injury  done  to  the  original.  Several  wood  engravings 
and  copper  plates  were  subjected  to  similar  treatment,  and 
are  now  in  process  of  being  deposited  on  in  the  apparatus 
before  me. 

'  I  now  come  to  the  third  and  concluding  portion  of  the 
experiments  on  this  subject,  the  object  being  to  deposit  a 
metallic  surface  on  a  model  of  clay,  wood,  or  other  non- 
metallic  body,  as  otherwise  I  imagined  the  application  of 
this  principle  would  be  extremely  limited.  Many  experi- 
ments were  made  to  attain  this  result,  which  I  shall  not 
detail,  but  content  myself  with  describing  those  which  were 
ultimately  most  successful. 

c 


1 8  The  A  rt  of  Electro-Metallurgy. 

'  I  procured  two  models  of  an  ornament — one  made  of 
clay,  and  the  other  of  plaster-of- Paris,  soaked  them  for  some 
time  in  linseed-oil,  took  them  out  and  suffered  them  to  dry. 
I  gave  them  a  thin  coat  of  mastic  varnish.  When  the  varnish 
was  nearly  dry,  but  not  thoroughly  so,  I  sprinkled  some  bronze 
powder  on  that  portion  I  wished  to  make  a  mould  of.  This 
powder  is  composed  of  mercury  and  sulphur,  or  it  may  be 
chemically  termed  a  sulphuret  of  mercury.  There  is  a  sort 
which  acts  much  better,  in  which  is  a  portion  of  gold.  I 
had,  however,  a  complete  metalliferous  coating  on  the  sur- 
face of  the  model,  by  which  I  was  enabled  to  deposit  a  sur- 
face of  copper  on  it  by  the  voltaic  method  I  have  already 
described.  I  have  also  gilt  the  surface  of  a  clay  model  with 
gold  leaf,  and  have  been  successful  in  depositing  copper  on 
its  surface.  There  is  another,  and,  as  I  trust  it  will  prove,  a 
similar  method  of  attaining  this  object ;  but,  as  I  have  not 
sufficiently  tested  it  by  experiment,  I  shall  take  another  op- 
portunity of  describing  it.'  The  reading  of  this  paper  was 
accompanied  by  an  exhibition  of  specimens  of  coins,  medals, 
and  copper  plates,  formed  by  the  electrotype  process. 

The  publication  of  Mr.  Spencer's  paper  excited  general 
attention,  and  thousands  of  persons  of  all  classes  of  society 
FIG  i.  at  once  became  fascinated  by  the  new 

art ;  and  various  improvements  were 
made  which  soon  led  to  its  becoming  a 
definite  manufacturing  process. 

The  apparatus  commonly  employed 
at  this  period  was  what  is  termed 
the  *  single  cell,'  and  is  shown  in  the 
annexed  figure,  in  which  A  is  a  wide, 
open  jar  of  glass  or  earthenware,  nearly 
filled  with  a  saturated  solution  of  blue 
vitriol  (sulphate  of  copper).  B  is .  a 
narrow  and  much  taller  jar,  made  of 
porous  earthenware,  containing  dilute  sulphuric  acid,  and 
filled  to  the  same  level  as  the  outer  vessel.  C  is  a  tall  rod  of 


Single-cell  Process.  1 9 

cast  zinc  immersed  in  the  acid,  and  supported  in  the  centre  of 
the  jar.  D  is  a  coin  or  medal,  suspended  in  the  copper  solution, 
and  attached  by  means  of  a  copper  wire  to  the  rod  of  zinc  ; 
and  E  is  a  perforated  copper  shelt  placed  near  the  top  of  the 
liquid,  upon  which  are  placed  crystals  of  blue  vitriol  to  sup- 
ply copper  to  the  solution  as  fast  as  it  is  extracted  by  the 
depositing  process.  For  the  circular  vessel  A,  and  round 
porous  cell  B,  and  cast  rod  of  zinc  C,  were  soon  afterwards 
substituted  rectangular-shaped  vessels,  which  are  more  con- 
venient, and  a  plate  of  rolled  zinc  coated  with  mercury. 

At  this  period  several  persons  were  attempting  to  make 
electro-plating  a  profitable  speculation.  Foremost  among 
these  were  Messrs.  G.  R.  and  H.  Elkington,  who  were  en- 
gaged commercially  in  the  year  1838  in  coating  military  and 
other  metal  ornaments  with  gold  and  silver,  by  simply  im- 
mersing them  in  solutions  of  those  metals,  particularly  a 
boiling  one  of  carbonate  of  potash  containing  dissolved  gold. 
They  also  employed  and  patented,  in  conjunction  with 
O.  W.  Barratt  (July  24, 1838),  a  process  for  coating  articles  of 
copper  and  brass  with  zinc,  by  means  of  an  electric  current, 
generated  by  a  piece  of  zinc  attached  to  the  articles  by  a 
wire,  and  immersed  with  them  in  a  boiling  and  neutral 
solution  of  chlonde  of  zinc.  This  was  the  first  patent  in 
which  a  separate  metal  was  employed  for  electro-plating 
purposes. 

During  the  year  1840  Mr.  John  Wright,  a  surgeon  in  Bir- 
mingham, and  Mr.  Alexander  Parkes,  an  experimentalist  in  the 
employment  of  Messrs.  Elkington,  were  engaged  in  electro-de- 
position experiments,  with  the  object  of  obtaining  with  gold 
and  silver,  similar  results  to  those  already  obtained  by  Jacobi, 
Jordan,  and  Spencer  with  copper,  viz.  thick  deposits  of  firm, 
coherent  metal,  bright,  and  of  good  colour.  As,  however, 
there  are  very  few  solutions  capable  of  yielding  such  results, 
their  attempts  were  not  at  first  completely  successful. 

At  this  juncture  Mr.  Wright  met  with  a  passage  in 
Scheele's  *  Chemical  Essays '  (pp.  405  and  406)  which  soon 

c  2 


2O  The  Art  of  Electro-Metallurgy. 

proved  of  the  highest  da  ree  of  importance  to  the  commer- 
cial success  of  the  art,  by  enabling  suitable  deposits  of  silver 
and  gold  to  be  obtained.  Speaking  of  the  solubility  of  the 
oxides  and  cyanides  of  gold,  silver,  and  copper,  Scheele  says 
'  If,  after  these  calces'  (i.e.  the  cyanides  of  gold  and  silver) 
'  have  been  precipitated,  a  sufficient  quantity  of  the  precipi- 
tating liquor  be  added  in  order  to  re-dissolve  them,  the  solu- 
tion remains  clear  in  the  open  air,  and  in  this  state  the 
aerial  acid '  (i.e.  the  carbonic  acid)  *  does  not  precipitate  the 
metallic  calx.' 

This  statement  suggested  to  Mr.  Wright  the  probable 
suitability  of  the  cyanides  of  gold  and  silver,  dissolved  in  so- 
lutions of  the  alkaline  cyanides,  for  the  purposes  of  electro- 
plating ;  and  he  immediately  took  a  solution,  composed  of 
chloride  of  silver  dissolved  in  aqueous  ferro-cyanide  of  potas- 
sium, and  quickly  obtained  what  had  never  been  acquired 
before,  viz.  a  thick  deposit  of  firm  and  white  silver  by  elec- 
trolytic action.  In  all  previous  trials  the  coating  of  silver 
had  either  been  very  thin,  or  in  a  state  of  dark-coloured, 
loose  powder,  completely  useless  for  the  intended  purpose. 

The  first  article  that  received  the  successful  coating  was 
a  small  vase,  and  the  next  was  a  small  figure  of  a  kid.  They 
were  coated  by  Mr.  Wright  at  his  residence,  and  the  process 
adopted  was  as  follows  : — A  common,  porous  garden-pot,  con- 
taining the  silver  solution,  was  placed  in  dilute  sulphuric  acid 
contained  in  an  outer  vessel ;  the  article  to  be  coated  was 
immersed  in  the  inner  liquid,  and  connected  by  a  wire  with 
a  cylinder  of  zinc  surrounding  the  porous  cell,  and  im- 
mersed in  the  dilute  acid.  It  was  about  a  month  after 
this  that  a  solution  of  actual  cyanide  (not  ferro-cyanide)  of 
silver  and  potassium  was  first  employed  by  Mr.  Wright  for 
the  same  purpose.  It  is  true  that  cyanides  in  several  forms 
had  been  used  both  for  electro-coppering  and  silvering  about 
sixteen  months  previously  ;  but  that  was  by  the  simple  im- 
mersion process,  without  the  use  of  zinc,  or  a  single  cell  or  bat- 
tery, and  by  that  process  no  thick  deposits  can  be  obtained. 


Discovery  of  Cyanide  Solution.  2 1 

Meanwhile  other  persons  were  active  in  other  depart- 
ments of  the  subject.  On  March  3,  1840,  Joseph  Shore 
patented  a  process  by  which  he  deposited  copper  from  a 
neutral  solution  of  its  sulphate,  and  nickel  from  one  of  its 
nitrates  '  kept  of  a  neutral  strength/  by  connecting  the  articles 
by  a  copper  wire  with  a  piece  of  zinc  in  dilute  sulphuric 
acid  ;  the  two  liquids  being  separated  by  a  partition  of  un- 
glazed  earthenware.  '  Larger  articles  are  covered  separately, 
and  small  articles,  such  as  iron  nails,  are  placed  in  a  wire 
basket  connected  by  a  wire  to  a  zinc  plate,  and  are  moved 
from  time  to  time  to  prevent  any  parts  remaining  uncovered.' 

At  this  period  Messrs.  G.  R.  and  H.  Elkington  were 
taking  out  another  patent,  dated  March  25,  1840,  for  an 
electro  process  for  coating  articles  with  silver  or  gold  by 
means  of  the  single-cell  arrangement,  using  solutions  com- 
posed of  oxide  of  silver  dissolved  in  '  pure  ammonia,'  or 
prussiate  of  soda,  or  other  analogous  salts  ;  or  oxide  of  gold 
dissolved  in  '  prussiate  of  potash '  by  boiling,  and  kept  '  satu- 
rated with  gold,'  or  in  *  any  soluble  prussiate,'  or  *  any  other 
analogous  salt.'  Mr.  Wright  having  submitted  his  results  to 
Messrs.  Elkington,  these  were  also  embodied  by  them  in 
their  patent.  At  first  Mr.  Wright  received  a  royalty  of  ore 
shilling  per  ounce  for  every  ounce  of  silver  deposited ;  but 
on  his  decease,  which  took  place  soon  afterwards,  an  annuity 
was  paid  to  his  widow.  This  patent  process  proved  to  be 
the  basis  of  all  successful  electro-plating  of  gold  and  silver, 
because  it  included  the  solutions  of  alkaline  cyanides,  the 
only  known  liquids  that  fulfil  all  the  necessary  conditions  ; 
and  the  success  of  those  liquids  was  largely  due  to  their 
alkaline  character.  From  the  earliest  period  of  electro- 
plating, german-silverwas  the  substance  employed  for  forming 
the  articles  which  were  to  be  plated. 

On  December  8  in  the  same  year  Messrs.  Elkington  took 
out  a  similar  patent  in  France ;  and  this  was  quickly  fol- 
lowed, on  December  19,  by  a  patent  taken  out  in  the  same 
country  by  M.  De  Ruolz,  a  French  electro-depositor,  for 


22  The  A  rt  of  Electro-Metallurgy. 

similar  objects  effected  by  similar  means,  viz.  electro-gilding 
by  means  of  a  solution  composed  either  of  cyanide  or  chlo- 
ride of  gold  dissolved  in  the  simple  cyanide,  the  ferro-cyanide 
or  the  ferrid-cyanide  of  potassium  ;  the  double  chloride  of  gold 
and  potassium  dissolved  in  cyanide  of  potassium  ;  the  double 
chloride  of  gold  and  sodium  dissolved  in  soda  ;  or  the  sul- 
phide of  gold  dissolved  in  neutral  sulphide  of  potassium  ; 
also  electro-silvering  by  means  of  a  solution  of  cyanide  of  silver 
dissolved  in  cyanide  of  potassium,  each  liquid  being  acted 
upon  by  means  of  the  voltaic  battery.  His  patent  also  included 
similar  solutions  for  the  electro-deposition  of  platinum,  cop- 
per, lead,  tin,  cobalt,  nickel,  and  zinc  ('Encyclopedic  Roret,' 
Galvanoplastie,  tome  ii.,  p.  114).  A  Commission  of  the 
French  Royal  Academy  of  Sciences  was  appointed  to  report 
on  the  new  processes  of  Elkington  and  De  Ruolz,  and  de- 
cided in  favour  of  Elkington.  A  dispute  also  arose  between 
the  two  patentees,  which,  after  a  trial  at  law,  was  finally  set- 
tled by  a  compromise. 

The  chief  conditions  of  success  in  the  process  had  now 
been  attained  by  the  use  of  the  cyanides,  but  there  still  re- 
mained various  smaller  difficulties  to  be  overcome.  In  some 
instances  the  deposited  silver  would  rise  in  blisters,  or  por- 
tions would  peel  off  on  application  of  the  burnishing  tool. 
Tn  others  the  metal  assumed  objectionable  colours,  frequently 
brown,  yellowish,  streaky,  or  grey  ;  or,  instead  of  being  even 
and  smooth,  it  was  covered  with  asperities,  nodules,  lines,  or 
vertical  grooves  ;  or  was  of  unequal  thickness.  Great  diffi- 
culty was  also  experienced  in  coating  articles  of  iron,  steel, 
lead,  Britannia-metal,  £c.,  so  as  to  secure  perfect  adhesion  ; 
and  particularly  in  coating  of  an  uniform  colour  and  appear- 
ance, articles,  the  different  parts  of  which  were  formed  of 
several  of  these  metals,  or  which  had  been  united  by  different 
kinds  of  solder.  In  consequence  of  these  various  defects,  par- 
ticularly imperfect  adhesion  and  blisters,  multitudes  of  articles 
were  returned  to  the  platers.  Great  opposition  was  also 
experienced  from  the  manufacturers  of  Sheffield  wares,  and 


Early  Difficulties  of  Electro-plating.  23 

shopkeepers  who  sold  plated  goods,  to  the  introduction  of 
the  new  articles  ;  and  in  consequence  of  these  various  diffi- 
culties the  process  was  not  remunerative  for  at  least  seven 
years. 

The  want  of  adhesion  between  the  silver  and  the  metal 
beneath,  arose  partly  from  the  employment  of  too  many  cells 
in  the  battery,  but  chiefly  from  want  of  perfect  cleanliness 
of  the  receiving  surfaces.  It  was  eventually  overcome  by 
cleaning  the  surfaces  with  very  great  care,  dipping  the 
cleaned  article  in  a  very  weak  solution  of  mercury  imme- 
diately before  placing  it  in  the  depositing  liquid,  and  lessening 
the  number  of  battery  cells.  Non-adhesion  of  the  silver  was 
especially  apt  to  occur  with  articles  made  of  Britannia  metal, 
and  with  this  particular  alloy  it  was  not  overcome  for  several 
years  ;  it  was  then  remedied  by  first  coating  the  surfaces 
with  copper,  by  electro-process,  in  a  liquid  composed  of 
cyanide  of  copper  dissolved  in  a  boiling  solution  of  cyanide 
of  potassium,  and  then  silvering  them.  This  method  was 
patented  by  O.  W.  Barratt,  September  8,  1841  ;  a  different 
and  a  simpler  process  is  now  employed. 

One  of  the  next  important  additions  to  the  art  of  electro- 
metallurgy was  that  made  by  Mr.  Murray  (January  1840) ; 
who  communicated  it  orally  to  the  members  of  the  Royal 
Institution,  London.  It  consisted  in  coating  non-conducting 
surfaces  with  plumbago,  which  being  an  electric  conductor 
enabled  deposits  of  metal  to  be  formed  by  the  electro-process 
upon  the  surfaces  of  non-conductors,  and  thus  greatly  ex- 
tended the  sphere  of  usefulness  of  the  art.  During  the  same 
year  also  Professor  de  la  Rive  made  known  a  process  of 
electro-gilding  employed  by  him  in  the  year  1828  ;  he  gilded 
wires  of  platinum  and  silver  'by  employing  them  as  negative 
electrodes  in  a  solution  of  chloride  of  gold.'  (De  la  Rive's 
'Treatise  on  Electricity,'  vol.  iii.,  p.  546.) 

In  the  same  year  also  another  arrangement  of  electro- 
depositing  apparatus,  now  known  as  the  '  separate  battery ' 
apparatus,  was  devised  by  Mr.  Mason.  In  this  new  arrange- 


24  The  Art  of  Electro- Metallurgy. 

ment  a  current  from  a  single  cell  of  a  DanielFs  battery,  A,  is 
caused  to  produce  deposition  in  a  separate  vessel,  B.  It  is 
represented  by  the  annexed  sketch. 


FIG.  2. 


In  this  apparatus,  as  fast  as  the  metal  is  removed  from 
the  solution  at  the  negative  pole,  by  articles  being  coated,  it 
is  replaced  by  an  equal  amount  of  metal  dissolving  at  the 
positive  pole,  or  dissolving  plate,  and  the  solution,  therefore, 
does  not  require  any  additional  supply  of  metallic  salt.  A 
still  further  modification  of  Mr.  Mason's  arrangement  was 
soon  generally  adopted,  by  substituting  any  ordinary  voltaic 
battery  for  the  single  cell  of  Daniell. 

Another  arrangement,  termed  the  'compound  depositing 
cell,'  was  also  devised  about  this  time,  by  means  of  which 

FIG.  3. 


the  current  from  a  single  cell,  A,  of  a  battery  was  caused  to 


Separate  Battery  Process.  2$ 

pass  through  a  series  of  depositing  cells,  B  (see  sketch),  and 
thus  dissolve  and  deposit  several  times  the  amount  of  metal 
by  the  same  amount  of  consumption  of  zinc  and  acid  ;  but  it 
was  soon  abandoned  on  account  of  the  slowness  of  action. 

During  the  year  1841  Mr.  Alfred  Smee  published  the 
results  of  his  experiments  upon  the  electro -deposition  of 
Antimony,  Iridium,  Rhodium,  Palladium,  Platinum,  Gold, 
Silver,  Copper,  Nickel,  Iron,  Lead,  Cadmium,  Zinc,  &c.,  in 
the  first  edition  of  his  book  on  Electro-metallurgy  ;  he  also 
applied  the  very  appropriate  term  *  electro-metallurgy  '  to  the 
process  of  working  in  metals  by  means  of  electrolysis.  In  the 
same  year  also  M.  De  Ruolz  electro-deposited  brass  from  a 
solution  composed  of  the  cyanides  of  copper  and  zinc  dis- 
solved in  aqueous  cyanides  of  potassium  (Walker's  '  Electro- 
type Manipulation,'  last  edition).  In  the  year  1841  also 
Alexander  Jones  took  out  a  patent  (dated  January  14) 
relating  to  electro-deposition,  in  which  he  renders  a  non- 
conducting surface  conducting,  and  fit  for  receiving  electro- 
deposits,  by  first  immersing  the  article  in  a  solution  of  nitrate 
of  silver,  then  reducing  a  film  of  silver  upon  it  by  means  of 
a  solution  of  green- vitriol,  or  by  phosphorus  either  in  solution 
or  vapour  ;  or  by  coating  the  surface  with  bronze  powder 
or  metallic  leaf. 

The  next  event  of  importance  in  the  history  of  electro- 
plating consisted  in  the  application  of  magneto- electricity  to 
that  object.  On  August  i,  1842,  J.  S.  Woolrich  took  out 
a  patent  for  the  use  of  a  magneto-electric  machine  in  electro- 
plating, and  this  machine  was  used  during  many  years  in 
several  electro -plating  establishments,  but  has  since  been 
quite  superseded  by  other  magneto-machines  of  an  improved 
kind.  During  the  same  year  Mr.  Palmer  patented  his  '  im- 
provements in  producing  printing  and  embossing  surfaces/ 
and  employed  electro-deposition  for  producing  the  copper 
plates ;  the  process  was  termed  '  Glyphography.'  Dr.  H.  R. 
Leeson  also  took  out  a  patent  on  June  i,  in  the  same  year, 
for  improvements  in  electro-metallurgy,  and  claimed  no  less 


26  The  A  rt  of  Electro-Metallurgy. 

than  about  430  (!)  different  salts  for  the  purposes  of  deposi- 
tion. He  suggested  '•  elastic  moulds/  formed  of  glue  alone 
or  glue  mixed  with  gum,  for  receiving  deposits  ;  also  *  posi- 
tive wires '  led  into  cavities  or  under  cut  parts  of  the  moulds, 
and  inserted  '  conducting  wires  in  wax  moulds  to  facilitate 
deposition  ; ;  and  proposed  to  keep  the  articles  to  be  coated 
constantly  in  motion  '  by  means  of  a  roasting-jack/  or  to 
'agitate  the  solution/ 

The  first  use  of  thermo-electricity  appears  to  be  that 
made  by  Moses  Poole,  who  took  out  a  patent,  dated  May 
25,  1843,  for  the  use  of  a  thermo-electric  pile  instead  of  a 
voltaic-battery  for  depositing  purposes.  The  method,  how- 
ever, did  not  come  into  general  use.  During  the  following 
year  (viz.  1844)  a  patent  was  taken  out  by  Napier,  dated 
October  22,  and  one  by  Parkes,  dated  October  29.  for  elec- 
tro-depositing metals  from  mineral  ores  and  salts  whilst  in  a 
state  of  fusion. 

The  next  improvement  arose  in  a  singular  way.  The 
surface  of  silver  deposited  from  the  ordinary  cyanide  of  silver 
and  potassium  plating  solution  has  a  frosted  or  snow-white 
appearance,  and  is  more  or  less  '  chalky '  and  dull,  and  re- 
quires to  be  burnished  or  made  bright  by  mechanical  means. 
This  with  articles  of  highly  figured  design,  or  which  are 
hollow  and  require  the  interior  to  be  bright,  is  a  great  disad- 
vantage, because  the  process  of  burnishing  is  tedious,  and 
when  it  has  to  be  applied  to  the  interior  of  vessels  it  is  also 
very  awkward  to  perform.  As  with  the  difficulty  of  obtain- 
ing thick  deposits  of  firm  silver  during  the  early  period  of 
the  electro-process  a  little  circumstance  led  to  that  obstacle 
being  overcome,  so  was  it  with  this  difficulty,  and  it  hap- 
pened as  follows  : — In  the  process  of  copying  figures  for 
electro-typing,  by  moulds  composed  of  a  mixture  of  wax  and 
resin,  the  surface  of  the  mould  was  covered  with  a  film  of 
phosphorus  by  means  of  a  solution  of  phosphorus  in  bisul- 
phide of  carbon.  It  was  observed  by  Mr.  W.  Milward,  at 
Messrs.  Elkington's  establishment,  that  when  these  mouLls 


Discovery  of  Bright -plating.  27 

were  put  into  the  cyanide  of  silver- plating  solution,  for  the 
purpose  of  receiving  a  coating  of  silver,  the  silver  coating 
upon  other  articles,  such  as  spoons,  forks,  &c.,  which  were 
being  plated  in  the  same  vats,  and  especially  those  nearest 
to  the  moulds,  acquired  a  brightness  more  or  less  perfect, 
which  occurred  sometimes  in  patches  or  streaks,  and  some- 
times extended  all  over  the  deposited  surface,  instead  of  the 
ordinary  snow-white  appearance.  This  circumstance  of 
course  attracted  attention,  and  induced  Mr.  Milward  to  try 
the  effect  of  adding  bisulphide  of  carbon  alone  to  the  liquid. 
Considerable  success  soon  resulted  ;  but  at  this  juncture 
the  secret  escaped,  and  in  consequence  a  patent  was  taken 
out  March  23,  1847,  by  Mr.  Milward  and  a  person  of  the 
name  of  Lyons,  who  had  acquired  a  kr  owledge  of  the  secret, 
for  producing  bright  deposited  silver  by  *  adding  compounds 
of  sulphur  or  carbon,'  bisulphide  of  carbon  being  preferred, 
to  the  cyanide  of  silver  solution.  This  process  has  been 
constantly  employed  ever  since,  and  is  now  in  extensive  use. 
Bright  copper  had  also  been  observed  about  the  year  1845, 
and  occurred  whenever  a  large  number  of  phosphorised  wax 
moulds  were  put  into  a  solution  of  sulphate  of  copper  to  re- 
ceive an  electro-deposit  of  copper.  In  the  year  1847  also, 
Professor  Silliman  copied  the  iridescent  colours  of  mother- 
of-pearl,  by  taking  a  mould  of  the  shell  in  fusible  alloy,  and 
then  an  electro-cast  from  the  mould  (*  Timbs'  Year- Book  of 
Facts,'  1847). 

Tiie  chief  improvements  which  have  been  made  in 
electro-metallurgy  since  the  year  1847  have  been  the  gradual 
extension  of  the  process  for  multiplying  printing  surfaces,  in 
stereotyping,  £c.,  also  the  production  of  works  of  art,  &c., 
of  increased  size  in  copper,  until  deposits  several  tons  in 
weight  have  been  attained  ;  the  extensive  use  of  nickel  as  a 
coating  upon  harness  furniture,  &c.,  the  protection  of  articles 
of  cast-iron,  ornamental  lamp-posts,  &c.,  from  rusting,  by  a 
coating  of  copper  ;  the  substitution  of  magneto-electric 
machines,  and  thermo-electric  piles,  for  voltaic  batteries  ;  the 


2  8  The  A  rt  of  Electro-Metallurgy. 

purification  of  crude  copper  in  the  process  of  copper  smelting; 
and,  quite  recently,  the  economical  production  of  coppered 
iron  rollers  for  calico  printing  by  means  of  magneto-electric 
deposition. 


THEORETICAL  DIVISION. 

PRINCIPLES   AND   LAWS   UPON   WHICH   THE   ART  OF 
ELECTRO-METALLURGY    IS   BASED. 

THE  phenomena  which  occur  in  electro-metallurgical  pro- 
cesses largely  involve  the  principles  of  dynamic  electricity, 
chemico-electric  action,  electro -chemical  action,  and  also  or- 
dinary chemical  affinity  ;  and,  if  magneto-electric  and  thermo- 
electric apparatus  are  also  employed,  the  phenomena  then 
include  also  magneto-electric  and  thermo-electric  action. 

Electric  conduction  and  insulation  are  involved  in 
electro-metallurgical  processes,  because  through  all  the  con- 
ductors, electric  generators,  and  depositing  liquids,  elec- 
tricity is  continually  circulating,  and  requires  to  be  guided  in 
its  course,  and  protected  from  leakage. 

Chemico-electric  action,  or  electric  change  produced  by 
chemical  power,  is  included,  because  that  action  is  always 
occurring  in  the  voltaic  batteries  employed.  Electro- 
chemical action  is  also  involved  because  that  change  is 
constantly  going  on  in  the  depositing  solutions.  In  the  mag- 
neto-machine, magneto-electric  induction  occurs  all  the  time 
the  machine  is  at  work  ;  and  in  the  thermo-electric  pile, 
thermo-electric  action,  or  heat  producing  electric  force, 
operates  without  cessation.  It  is  evident,  then,  that  a  clear 
perception  of  the  principles  of  these  actions  is  indispensably 
necessary  to  a  proper  understanding  of  the  subject. 

ELECTRICAL   PRINCIPLES   OF   ELECTRO-METALLURGY. 

Conduction  and  insulation. — Conducting  and  insulating 
power  for  electricity,  or  the  capacities  of  facilitating  and 


Conduction  and  Insulation.  29 

hindering  the  passage  of  electricity,  differ  in  degree  in  every 
different  substance.  The  best  conductor  is  the  worst  insu- 
lator, and  vice-versa,  the  degree  of  the  one  property  being 
inverse  to  that  of  the  other  in  every  substance.  All  bodies 
conduct  electricity,  but  in  different  degrees,  and  all  insulate 
also  in  different  degrees,  and  the  difference  of  conducting 
power  of  the  best  conductor  in  relation  to  that  of  the  worst 
is  enormous  ;  and  similarly  with  regard  to  insulating  power. 
The  following  is  a  table  in  which  various  common  sub- 
stances are  ranged  approximately  in  the  order  of  their 
relative  power  of  insulating,  or  hindering  the  passage  of 
electricity ;  it  commences  with  the  most  perfect  insulators, 
and  ends  with  the  best  conductors  : — 

1.  Ebonite.  20.  Chalk. 

2.  Shellac.  21.  Lime. 

3.  Caoutchouc.  22.  Dry  gases. 

4.  Gutta-percha.  23.  Dry  steam. 

5.  Amber.  24.  Phosphorus. 

6.  Resin.  25.  Fatly  oils. 

7.  Sulphur.  26.  Dry  metallic  oxides. 

8.  Wax.  27.  Iceato°C. 

9.  Agate.  28.  Straw. 

10.  Glass.  29.  Paper. 

11.  Gems.  30.  Marble. 

12.  Silk.  31.  Dry  wood. 

13.  Wool.  32.  Alcohol.     Ether. 

14.  Hair.  33.  Rain-water. 

15.  Feathers.  34.  Spring- water. 

16.  Dry  paper.  35.  Sea-water, 

17.  Leather.  36.  Graphite. 

18.  Porcelain.  37.  Brittle  metals. 

19.  Camphor.  38.  Ductile  metals. 

The  difference  of  insulating  power  or  conduction-resist- 
ance between  the  substances  at  the  two  extreme  ends  of  the 
table  is  extremely  great.  If  the  resistance  of  silver  to 
the  passage  of  the  current  be  represented  by  i,  that  of  a 
rod  of  gutta-percha,  of  equal  length  and  diameter,  has 


3O  The  Art  of  Electro-Metallurgy. 

been  estimated  to  equal  about  850,000,000,000,000,000,000. 
Ths  insulating  substances  usually  employed  in  electro- 
metallurgy are  either  gutta-percha,  glass,  or  india-rubber, 
and  the  wire  employed  in  magneto-electric  machines  is 
insulated  by  being  covered  with  cotton  or  silk.  The  large 
conductors,  to  supply  the  main  currents  to  the  vats,  are 
covered  with  gutta-percha  or  tarred  twine.  The  wires  for 
suspending  spoons,  forks,  &c.,  in  the  solutions  are  enclosed 
in  tubes  of  glass. 

The  relative  conducting  powers  of  pure  metals,  &c.,  ac- 
cording to  Dr.  Matthiessen,  are  as  follows :  — 


Silver  ....  locro 

Copper         .         .         .  99-9 

Gold    .        .         .  77 -9 

Zinc     ....  29-0 

Cadmium     .         .         .  23-7 

Palladium     .         .         .  18-4 

Platinum      .         .         .  i8'O 

Cobalt          .         .         .  17-2 

Iron     ....  16-8 

Nickel          .         .         .  13-1 


Tin    .  .  .  .     12-4 

Thallium  .  .  .9-2 

Lead.  .  .  .8-3 

Arsenic  .  .  .4-8 

Antimony  .  .  .4-6 

Mercury  .  .                 i'6 

Bismuth  .  .  .        I P2 

Graphite  .  .  .         "069 

Gas  coke  .  .  .         -038 

Bunsen's  coke  .  .          '025 


Copper  being  the  cheapest  good  conductor,  very  flexible 
and  ductile,  easily  obtainable,  and  not  readily  oxidised,  is 
nearly  always  employed  for  transmitting  the  current  in  elec- 
tro-metallurgical operations.  Wire  composed  of  iron  or  of 
brass  is  rarely  used  for  such  a  purpose. 

The  conductivity  of  fused  salts  varies  greatly  ;  if  that  of 
mercury  equals  100,000.000,  that  of  chloride  of  lead  is 
25,300;  of  iodide  of  potassium  11,500  •  of  nitrate  of  silver 
8,688  ;  of  common  salt  8,660  ;  of  potassic  carbonate  2,150  ; 
and  of  chloride  of  zinc  86  (F.  Braun,  '  Chemical  News,' 
vol.  xxx.  p.  207). 

The  conduction-resistances  of  liquids  are  enormous 
in  comparison  with  those  of  metals.  For  instance,  if  that  of 
copper  at  32°  Fahr.  is  equal  to  i,  those  of  various  liquids  are 
as  follows  : — 


Conduction-Resistance.  3 1 

Nitric  acid  at  55°  Fahr 976,000 

Sulphuric  acid  diluted  to  T\  at  68°  Fahr.      .         .         .  1,032,020 

Saturated  solution  of  chloride  of  sodium  at  56°  Fahr.   .  2,903,538 

,,              ,,         sulphate  of  zinc          .         .         .  15,861,267 

„              „                  „       copper  at  48°  Fahr.  .  16,885,520 

Distilled  water  at  59°  Fahr 6,754,208,000 

According  to  Dr.  Overbeck,  if  the  resistance  of  water 
equals  390,  that  of  alcohol  is  13,000,  of  ether  40,000,  and  of 
bisulphide  of  carbon  still  greater.  Small  additions  of  saline 
matters  greatly  diminish  the  resistance  of  water  ('  Electrical 
News,'  vol.  i.,  p.  170). 

If  the  conduction-resistance  of  distilled  water  is  so  great 
in  relation  to  that  of  copper,  we  can  easily  understand,  by 
referring  to  the  previous  table,  that  the  resistance  of  gases 
must  be  enormous.  The  electric  conduction-resistance  of  air 
heated  to  redness  is  30,000  greater  than  that  of  water,  con- 
taining a  2o,oooth  part  of  its  weight  of  sulphate  of  copper 
in  solution.  The  ordinary  unit  of  electrical  resistance  em- 
ployed in  this  country  is  termed  an  'Ohm*  (see  Jenkin's 
'Treatise  on  Electricity  and  Magnetism,'  p.  158;  also 
Appendix,  p.  387  of  this  book). 

Effects  of  temperature,  purity,  6*r.,  upon  the  electric  con- 
ductivity of  substances.  —The  conducting  power  of  substances 
is  largely  affected  by  their  degree  of  purity.  The  least 
admixture  of  a  foreign  substance  in  a  metal  has  a  great 
effect ;  arsenic  in  copper  is  very  injurious  to  electric  con- 
duction, and  may  even  increase  the  resistance  as  much  as 
66  per  cent. ;  while  one  half  per  cent,  of  iron  increases  the 
resistance  of  copper  as  much  as  25  per  cent. 

The  conducting  powers  of  bodies  are  also  greatly  in- 
fluenced by  temperature.  Warming  a  metal  increases  its 
conduction-resistance.  Metals  usually  lose  about  30  per 
cent,  of  conducting-power  by  rise  of  temperature  from  o°  C. 
to  100°  C. ;  german-silver,  however,  loses  only  about  4  per 
cent,  by  that  change.  Solid  non-metallic  substances  usually 
increase  in  conducting  power  with  rise  of  temperature  ;  so  also 
do  liquids  almost  uniformly,  and  gases  very  considerably. 


32  Tfo  Art  of  Electro-Metallurgy. 


of  conductfe^re«*tance  are  at  present 
rardy  made  in  electro-iBetaflurgkal  operation*,  but  a* 
*cjence  extend*  they  win  probably  require  to  be,  The  de- 

a  wire  rarie*  directly  a*  it* 


and  inrer*ety  a*  the  ate*  of  it*  cro***ectioiL  Adds 
aod  **Jine  liquid*  obey  die  *ame  law*  of  conduction  in  th  b 
respect  a*  metal*,  'tfe  m&hod*  o(  w&wrtmcnt  <rf  c\&xrv, 
condijction^eftrtance  are  fiifly  defcribed  in  die  treati*e  on 
'Electricity  and  Magnetwm,'  p,  129,  bf  jReemtng  Jenksn, 

/Av/          ,        •        „    •-.  '         -    •     'V  ",  //  '/,,    /-/-././ 

tf/x^  —  A¥  beat  can  produce  electrkity,  foefectrlctty  car/ 
dace  beat.    It  i«  a  general  troth  of  electrical  0cJence,  diat 
wherever  an  electric  current  overcome*  refinance  it  produce* 
beat  An4ittbere*orenottinfre<|iientty 


condtfctlng  wire*,  deponing  foftttionf  f  the  coilf  of 
wire  in  magneJo*eJeclric  madiine*,  die  cooler  junction*  of 

'•  •.".-,'.  '."-.-.'    ;>  .'•.,  -V   ;  •/",-:.'    r:.o."    V  .<  ..  ;.•:;"/;  /   :,:.': 

the*e  ctfctnmtance*  anect  die  working 

Efatrv'Chtmi&il  atthm.—'fte  Amdamentai  baff*of  etec* 
tro-metaJ  J  ur^y  i*  die  Act  that,  «x^w  «  current  of  electricity 

thrwth  a  tuitabU  liquid,  it  product!  a  chemical  cfi<> 
Tbi*  phenomenon  I*  called  electro^iemical  action,  becau*e 
elec^citf  »  die  cau*ef  and  chemical  action  die  «•' 
The  chief  condition*  of  electro-chem^  action  are  that  the 
Mbftance  mo*t  be  a  liquid,  a  compound  body,  a  conductor 
•  Mrix.it  y,  and  traveled  by  the  current/    An  electrolyte 
(*ee  p/  33;  i*  uttially  compoied  of  two  elementary  *ub*tance* 
-^the  one  a  conductor,  and  die  other  ation<ondfictor  of  elec^ 
tricity  ;  a  frjuid  which  i*  compo*ed  either  of  two  conductorf 

iuctor*  doe*  not  u*ua)Jy  *uner  electroly*i*, 
The  chemical  change  which  take*  place  con*i*t*  of  a 
chemical  decompofltion  of  the  liquid  ;  and  die  con*tituent* 
o^  the  liquid—  either  primary  or  *econdary—  *re  liberal 
A  free  *tate/    The  *ub*tance*  are  liberated  not  in  the  ma** 
v  liquid,  but  at  the  immediate  lur/aeet  0f  tonlact  of  the 


33 

liquid  with  the  conductors,  by  which  the  current  enters  and 

,  e  to  which  the  ju 
o  of  the  conductor  into  the  mass  of 
the  liquid,  is  so  extremely  small,  as  not  to  be  definitely 

^s  of  electrolysis  the  electro-negative  dements 

of  the  tiquivl.  such  as  metalloids  and  acids,  either  combine 

with,  or  are  set  free,  at  the  surface  of  the  dissolving  or 

posit  -d  the  electro-positive  elements,  such  as 

metals  and  alkalies,  either  combine  \\ith,  or  are  set  free  or 

e  of  the  receiving  or  r  cUl 

For  instance,  if  a  piece  of  silver  and  a  piece  of  c\ 

immersed  in  a  solution  of  sulphate  of  copper,  and  the  current 

from  a  battery  be  passed  into  the  solution  by  means  of  the 

piece  of  copper,  and  out  of  it  by  means  of  the  silver,  the  ne~ 

^  o  dements  of  the  liquid,  vi*  the  sulphuric  acid  of  the 

sulphate  of  copper,  will  be  separated  from  its  tstt 

copper,  and  will  combine  with  the  positive  copper  terming 

\e  in  the  liquid;  while  the  positive  ete* 

of  the  liquid,  vi*  the  copper  of  the  salt,  will  be  v 

'c  surface  of  the  negative  or  receiving  metal  the  -il- 
ut  will  not  combine  with  it   But  if  \ve  sul>stitute  a 

the  piece  of  copper,  and  mcrvurv  for  the  si 
-  will  be  reversed  $  the  acid  or  negative  element  will 
colWv  ,:  the  positive  platinum,  but  will  not  <xmU>ine 

.  •  ••  \t  of  the  liquid,  t he  wp)*cr» 
^     t>e  deposited  and  combine  with  the  n 

JfommJAfitrt  </«*«^H^W^U/  <wtfr**~ The  phenome- 
d  decomposition  of  a  h\m  an 

ACtordance  with  the  nomenclature 
ted  by  Faratfey»  who  specially  investi^ated  it,  v\dle\l 
The  liquid  in  which  .die  I  an 

The  conducH>rs  immersevl  in  the  liquid » 

^  »wA^\t  t  h .  !  oallevl  the  4W*MK  v  i 

pole,  and  0\»  .^^the  ^lutioi\  is  tcrmcvl  the 


34  The  A  rt  of  Electro-Metallurgy. 

cathode,  or  negative  pole.  The  elements  of  the  liquid  which 
are  set  free  by  the  action,  are  called  ions  ;  those  which 
appear  at  the  anode,  or  positive  pole,  are  called  anions,  and 
those  at  the  cathode,  or  negative  pole,  cations. 

Usual  phenomena  of  electrolysis. — The  effects  which  take 
place  at  tne  two  electrodes  appear  in  various  forms  ;  in  some 
cases  a  gas  is  set  free  and  ascends,  or  it  adheres  in  bubbles 
all  over  the  front  surfaces,  and  round  the  edge  s  of  the  elec- 
trode, or  is  absorbed  by  the  electrode  ;  in  other  instances  a 
solid  substance  is  formed,  and  either  adheres  to  the  electrode, 
foils  to  the  bottom  of  the  liquid,  or  enters  into  solution. 
Usually  the  anode  dissolves  and  gradually  becomes  thinner ; 
sometimes  streams  of  liquid  are  seen  slowly  falling  from  the 
anode  to  the  bottom,  or  rising  from  the  cathode  to  the  surface 
of  the  solution,  caused  by  the  alteration  of  specific  gravity 
of  the  layers  of  liquid  in  contact  with  the  electrodes,  by 
means  of  electrolysis.  Various  special  phenomena  also  occur 
in  particular  cases,  which  will  be  mentioned  under  the  heads 
of  the  deposition  of  individual  substances. 

Decomposability  of  different  electrolytes. — Different  liquids 
require  very  different  degrees  of  electric  power  to  decompose 
them.  Faraday  has  given  the  following  order  with  the  sub- 
stances here  mentioned,  the  first  named  being  the  most 
easily  decomposed  : — Solution  of  iodide  of  potassium  ; 
melted  chloride  of  silver ;  melted  chloride  of  zinc  ;  melted 
chloride  of  lead  ;  melted  iodide  of  lead  ;  hydrochloric  acid  ; 
dilute  sulphuric  acid.  Smee,  in  his  '  Elements  of  Electro- 
Metallurgy,'  2nd  edition,  p.  185,  gives  nitric  acid  as  the 
most  easily  decomposable  liquid,  and  other  substances  in  the 
following  order  : — 

Nitric  acid.  Dilute  sulphuric  acid. 

Chloride  of  gold.  Sulphate  of  cadmium. 

Nitrate  of  palladium.  Sulphate  of  zinc. 

Chloride  of  platinum.  Sulphate  of  nickel. 

Nitrate  of  silver.  Sulphate  of  iron. 

Sulphate  of  copper.  Sulphate  of  manganese. 

Sulphate  of  tin.  Salts  of  the  alkalies,  generally. 


Direction  of  Electrolysis.  35 

I  have  many  times  observed  that  water  is  decomposed 
before  hydrofluoric  acid,  and  hydrochloric  acid  in  preference 
to  water  ;  also  selenic  acid  before  selenate  of  nickel ;  but  the 
order  of  decomposability  would  probably  be  affected,  both  by 
pressure,  temperature,  and  degree  of  dilution.  Much  investi- 
gation is  required  in  this  branch  of  the  subject. 

Direction  of  electrolysis. — In  the  electrolysis  of  any  given 
liquid,  the  substances  set  free  at  the  anode  are  always  rela- 
tively electro-negative  to  those  set  free  at  the  cathode,  and 
the  latter  of  course  are  relatively  positive.  Anions,  therefore, 
are  electro-negative  and  cations  are  electro-positive  sub- 
stances. The  negative  substances  appear  at  the  positive 
pole,  or  the  electrode  attached  to  the  copper  plate  of  the 
battery ;  and  the  positive  substances  at  the  negative  pole, 
or  the  electrode  attached  to  the  zinc  of  the  battery.  Metals, 
alkalies,  and  bases,  being  electro-positive,  are  cations,  and 
appear  at  the  negative  plate  ;  and  metalloids,  peroxides,  and 
acids,  being  electro-negative,  are  ani'ons,  and  appear  at  the 
positive  one.  As  the  condition*  of  positive  and  negative 
are  relative,  and  no  substance  is  absolutely  either,  the  same 
body  may  sometimes  appear  at  the  anode,  and  on  other  oc- 
casions at  the  cathode  ;  for  instance,  sulphur  when  separated 
from  a  positive  body,  such  as  a  metal,  appears  at  the  anode, 
but  when  liberated  from  oxygen,  a  more  negative  substance 
than  itself,  it  appears  at  the  cathode. 

Circumstances  which  affect  the  quality  of  electro-deposited 
metals  — The  physical  qualities  of  the  deposited  substances 
are  largely  affected  by  a  number  of  circumstances  ;  such  as 
the  composition  of  the  liquid,  its  degree  of  fluidity,  tem- 
perature, &c.,  also  the  ' density'  of  the  current,  or  the 
actual  quantity  of  electricity  entering  a  given  magnitude  of 
surface  in  a  given  'time  ;  the  rate  of  deposit ;  and,  further, 
the  condition  of  the  receiving  surface. 

The  terms  employed  to  designate  the  quality  of  the  de- 
posited metal  refer  usually  to  its  mechanical  state  and  colour. 


36  The  A  rt  of  Electro-Metallurgy. 

By  'reguline'1  metal  is  meant  that  which  possesses  the  ordinary 
or  more  perfect  metallic  qualities  of  the  metal :  thus  reguline 
copper  is  red,  bright,  and  tough ;  reguline  antimony  is  grey, 
hard,  and  crystalline ;  amorphous  antimony  is  without 
crystalline  structure.  The  terms,  crystalline,  sandy  metal, 
black  powder,  &c.,  are  also  frequently  used. 

Every  different  solution,  and  at  every  different  tempera- 
ture, requires  to  be  electrolysed  at  a  different  rate,  in  order 
to  deposit  its  metal  from  it  in  any  particular  desired  state 
of  aggregation,  as  crystals,  reguline  metal,  or  black  powder  ; 
and  this  is  further  modified  by  the  form  and  mechanical  state 
of  the  receiving  surface,  a  rough  surface,  or  one  covered 
with  points,  or  having  ragged  edges,  requires  a  slower  rate  of 
deposition  than  a  smooth  one,  in  order  to  obtain  regimne 
metal.  A  large  amount  of  experimental  investigation  remains 
to  be  made  also  in  this  part  of  the  subject. 

The  circumstance  which  most  affects  the  quality  (and 
purity)  of  the  deposited  metal  is  the  composition  of  the  elec- 
trolyte. By  far  the  greater  number  of  solutions  yield  up 
their  metal  only  in  the  form  of  a  black  powder,  however 
carefully  the  process  be  conducted.  From  only  a  very  few 
liquids  are  metals  deposited  in  their  ordinary  or  reguline 
state,  and  only  a  few  of  the  metals  have  yet  been  obtained  in 
that  condition  in  thick  masses.  Copper,  antimony,  and  silver 
are  the  easiest  to  obtain  in  thick  layers  ;  I  have  obtained 
reguline  deposits  of  antimony  IT?  inch  in  thickness.  Zinc, 
gold,  platinum,  tin,  nickel,  cadmium,  and  lead  are  usually 
only  obtained  in  thin  reguline  films,  or  in  roughly  aggregated 
nodules  or  crystalline  forms ;  and  most  of  the  other  metals 
have  been  only  obtained  in  the  state  of  a  dark  powder. 
The  degree  of  fluidity  and  diffusive  power  of  the  electrolyte 
also  affects  the  deposit ;  a  thick,  immpbile,  non-diffusive 
liquid  will  adhere  to  the  cathode  after  the  layer  next  that 
electrode  has  been  deprived  of  its  metal,  and  thus  alter  its 

1  The  term  '  reguline  '  differs  from  '  regulus  ; '  the  latter  means  metal 
which  has  been  reduced  from  its  ores  by  means  of  fusion  and  a  fiux. 


Qttality  of  Electro-Deposited  Metals.  37 

quality.  Some  solutions  also  will  only  yield  reguline  metal 
whilst  they  are  hot,  or  whilst  being  stirred. 

A  paper  was  read  at  the  meeting  of  the  British  Associa- 
tion, at  Bradford,  by  Dr.  Gladstone,  on  *  Black  Deposits  of 
Metals,'  in  which  he  remarks  that  the  allied  metals,  platinum, 
palladium,  and  iridium  are  generally,  if  not  always,  black 
when  precipitated  by  substitution  (i.e.  by  single  immersion 
process),  and  bismuth  and  antimony  form  black  fringes  and 
little  else  ;  similar  fringes  are  also  formed  by  gold  ;  but  it 
also  yields  green,  yellow,  or  lilac-coloured  metal  according 
to  circumstances.  Copper,  when  first  precipitated  on  zinc, 
whether  from  a  weak  or  strong  solution,  is  black  ;  but  in  the 
latter  case  it  becomes  chocolate-coloured  as  it  advances,  or 
red  if  the  action  be  more  rapid.  Lead,  in  like  manner,  is 
always  deposited  black  in  the  first  instance,  though  the  grow- 
ing crystals  become  of  the  well-known  dull  grey.  Silver  and 
thallium  appear  as  little  bushes  of  black  metal  on  the  de- 
composing plate  if  the  solution  be  very  weak,  otherwise  they 
grow  of  their  proper  colour.  Zinc  and  cadmium  give  a  black 
coating,  quickly  passing  into  grey  when  their  weak  solutions 
are  decomposed  by  magnesium.  The  general  result  may  be 
stated  thus  :  if  a  piece  of  metal  be  immersed  in  the  solution 
of  another  metal  which  it  can  displace,  the  latter  metal  imme- 
diately makes  its  appearance  at  myriads  of  points  in  a  con- 
dition that  does  not  reflect  light ;  but  as  the  most  favourably 
circumstanced  crystals  grow,  they  acquire  the  optical  proper- 
ties of  the  massive  metal,  the  period  at  which  the  change 
takes  place  depending  partly  on  the  nature  of  the  metal,  and 
partly  on  the  rapidity  of  its  growth  ('  Telegraphic  Journal,' 
vol.  i..  p.  302). 

Some  metals  are  especially  liable  to  crack  and  curl  up 
whilst  being  deposited  ;  this  is  the  case  in  a  strong  degree 
with  antimony,  and  less  so,  but  conspicuously,  with  iron  and 
nickel.  Others  form  very  hard  and  tenacious  deposits  ;  that 
of  iron  is  extremely  hard,  and  of  nickel  so  much  so  that  it 
cannot  be  burnished,  and  if  scratch-brushed  it  becomes  quite 


3  8  The  A  rt  of  Electro-Metallurgy. 

yellow  by  tearing  off  particles  of  the  brass  scratch-brushes. 
Electro-  deposited  copper,  and  even  gold,  is  also  sometimes 
remarkably  hard.  All  electro-deposited  metals  are  more  or 
less  crystalline  or  porous,  and  can  rarely  be  made  to  form 
air-tight,  or  even  water-tight,  vessels  without  annealing,  es- 
pecially if  the  layer  of  metal  first  deposited  is  scraped  or 
filed  away  ;  electro-deposits  therefore  do  not  protect  metallic 
surfaces  from  oxidation,  like  a  coating  of  the  same  metal  put 
upon  them  by  a  process  of  fusion.  They  are  also  more 
porous  on  their  outer  surfaces,  i.e.  the  side  last  deposited, 
than  upon  their  inner,  and  if  heated  in  a  fire  will  often  become 
concave  on  the  side  last  deposited.  Seams  also  cannot 
be  closed  (or  edges  joined  together)  by  electro-deposition  ; 
they  always  became  larger ;  even  a  scratch  will  gradually 
become  a  deep  groove. 

Influence  of  den sity  of  the  current. — Next  to  the  composi- 
tion of  the  liquid,  the  circumstance  which  most  affects  the 
quality  of  the  deposit  is  what  has  been  termed  the  '  density 
of  the  current,'  or  the  actual  quantity  of  electricity  entering 
a  given  area  of  receiving  surface  in  a  given  time.  With 
a  good  depositing  solution,  a  non-oxidisable  metal,  if  the 
density  of  the  current  is  great,  is  deposited  as  a  black  powder ; 
if  it  is  small  the  metal  assumes  the  form  of  crystals,  or  is 
precipitated  in  the  state  of  a  subsalt ;  and  between  these  two 
extremes,  the  soft,  reguline,  hard,  and  sandy  deposits  occur. 
A  saturated  solution  of  sulphate  of  copper,  acidulated  with 
dilute  sulphuric  acid,  yields  good  reguline  metal  when  the 
metal  is  deposited  from  it  at  the  rate  of  about  half  an  ounce 
per  square  foot  of  surface  per  hour.  The  density  of  the  cur- 
rent affects  not  only  the  quality  of  the  liberated  cations,  but 
also  that  of  the  anions,  as  has  been  already  observed  (see 
'  Telegraphic  Journal,'  vol.  ii.,  p.  178)  in  the  instance  of 
oxygen,  also  with  chlorine. 

The  effect  of  small  density  of  the  current  is  different 
with  solutions  of  the  noble  metals  to  what  it  is  with  those  of 
the  base  ones,  because  the  latter  metals  are  easily  oxidised 


Formation  of  Metallic  Crystals.  39 

and  the  former  are  not.  With  solutions  of  noble  metals 
a  current  of  small  density  deposits  the  metal  in  the  form  of 
crystals,  but  with  those  of  the  base  ones  it  deposits  an  oxide, 
or  even  a  subsalt,  instead  of  the  metal.  And  as  the  current 
is  strongest  at  its  first  commencement  and  is  then  weakened, 
first  by  polarisation  and  subsequently  by  the  deposition  of 
the  less-conducting  layer,  the  deposit  rapidly  changes  in 
many  cases  from  good  reguline  metal  to  a  non-adherent 
coating  of  oxide  or  salt.  Solutions  of  nickel  are  very  apt 
to  show  this  change  (p.  232). 

A  perfectly  smooth,  bright  surface  is  the  best  to  receive  a 
deposit ;  if  the  surface  is  rough  the  deposit  will  be  rough 
also.  As  a  deposit  increases  in  thickness  it  becomes  more 
and  more  uneven,  and  therefore,  in  nearly  all  cases,  the 
deposit  sooner  or  later,  and  in  most  cases  very  quickly,  loses 
its  reguline  character  and  brightness,  and  becomes  a  layer  of 
either  black  or  crystalline  powder  ;  the  edges  of  the  cathode 
which  receive  the  thickest  deposit -are  the  soonest  affected. 

Formation  of  metallic  crystals. — Every  different  metal, 
and  even  the  same  metal  when  deposited  from  different  solu- 
tions, gives  a  different  form  of  crystal.  In  some  solutions — 
chloride  of  tin  for  example — crystals  form  with  great  rapidity. 
The  annexed  figures  represent  the  forms  of  crystals  of  silver, 
tin,  and  gold  ;  they  are  copied  from  Dr.  Gladstone's  Lectures, 
1  Telegraphic  Journal/  vol.  iii.,  pp.  29  and  38.  Fig.  4  repre- 
sents silver  deposited  from  a  weak  solution  of  nitrate  of 
silver  ;  Fig.  5,  ditto,  from  a  strong  solution ;  Fig.  6,  from  a 
very  strong  solution  ;  Figs.  7  and  8,  from  a  nearly  exhausted 
solution  ;  and  Fig.  9  from  a  2\  per  cent,  solution.  Fig.  10 
shows  tin,  deposited  from  a  solution  of  chloride  of  tin  ;  and 
Fig.  n,  gold,  from  a  solution  of  chloride  of  gold. 

Circumstances  which  affect  the  quantity  of  electro- deposited 
metal. — In  a  liquid  which  yields  at  the  cathode  a  single 
metal  only,  the  quantity  of  the  particular  metal  set  free 
depends  entirely  upon  the  amount  of  electricity  which  has 
passed ;  but  with  different  metals  it  depends  also  upon  what 


40  The  Art  of  Electro-Metallurgy. 


Quantity  of  Electro-Deposited  Metals.  41 

is  termed  the  valency  of  the  metal  and  upon  its  atomic 
weight ;  by  valency  is  meant  the  amount  of  chemical  force 
associated  with  an  atom. 

This  part  of  the  subject  requires  on  the  part  of  the 
student  a  certain  amount  of  knowledge  of  chemistry  ;  and 
as  this  book  is  not  one  on  that  subject,  I  assume  that  the 
student  already  possesses  a  sufficient  preparatory  acquaint- 
ance with  chemistry  to  enable  him  to  enter  on  the  subject 
of  electro-metallurgy ;  that  he  is,  for  instance,  acquainted 
with  the  chief  properties  of  the  commoner  elementary 
substances,  and  of  their  chief  compounds  ,  of  acids,  bases 
and  alkalies ,  of  the  meaning  of  the  terms  specific  gravity, 
molecular  weight,  combining  and  equivalent  proportions, 
molecular  gaseous  volumes,  &c.;  but,  if  he  is  not,  I  must 
refer  him  to  Miller's  '  Inorganic  Chemistry,'  published  in  this 
series  of  text- books.  I  therefore  only  insert  in  this  treatise 
such  chemical  information  as  I  consider  must  not  be  omitted. 

Relation  of  chemical  value,  or  valency  cf  afows,  to  electro- 
lysis.— In  accordance  with  the  doctrines  of  chemistry,  the 
elementary  substances  are  classed  into  Monads,  Dyads, 
Triads,  Tetrads,  £c.,  as  in  the  following  table  : — 


MONADS 

DYADS 

TRIADS 

TETRADS 

HEXADS 

Hydrogen 

Oxygen 

Nitrogen 

Carbon 

Molybdenum 

Lithium 

Sulphur 

Boron 

Silicon 

Vanadium 

Fluorine 

Selenium 

Phosphorus 

Titanium 

Tungsten 

Chlorine 

Tellurium 

Arsenic 

Tin 

Osmium 

Bromine 

Barium 

Antimony 

Zirconium 

Chromium 

Iodine 

Strontium 

Rhodixim 

Thorinum 

Manganese 

Caesium 

Calcium 

Gold 

Cerium 

Rubidium  i   Lanthanum 

Bismuth 

Iron 

Potassium  i   Didymium 

Aluminium 

Nickel 

Sodium 

Glucinum 

Indium 

Cobalt      * 

Thallium 

Magnesium 

Uranium 

Silver 

Zinc 

Lead 

Cadmium 

Ruthenium 

Copper 

Iridium 

Mercury 

Palladium 

Platinum  • 

TJie  Art  of  Electro-Metallurgy. 


A  monad  is  an  elementary  substance,  one  atom  of  which 
possesses  one  equivalent  of  chemical  power ;  a  dyad  is  one, 
an  atom  of  which  possesses  two  such  equivalents  \  a  triad 
three  ;  a  tetrad  four,  &c.  One  atomic  weight  therefore  of 
a  dyad  element  is  chemically  equivalent  to  two  of  a  monad 
element ;  one  such  weight  of  a  triad  element  is  chemically 
equivalent  to  three  of  a  monad,  or  one  and  a  half  of  a  dyad  ; 
one  of  a  tetrad  is  equivalent  to  four  of  a  monad,  two  of  a 
dyad,  or  one  and  a  third  of  a  triad  ;  and  so  on. 

Equivalency  of  electro-chemical  action. — As  substances 
by  chemical  union  unite  in  certain  definite  proportions  by 
weight,  it  follows  as  a  matter  of  course  that  when  a  chem- 
ical compound  is  decomposed,  the  separated  ingredients 
must  also  possess  definite  proportions  by  weight.  When, 
therefore,  by  the  passing  of  a  current  of  electricity  through 
a  compound  conducting  liquid,  elementary  substances  are 
liberated  at  the  electrodes,  they  are  set  free  in  their  chemi- 
cally equivalent  proportions  by  weight.  And  as  the  chemi- 
cally equivalent  proportions  are  either  the  same  as  their 
atomic  weights,  or  are  some  simple  submultiple  of  them, 
the  following  table  of  atomic  weights  is  inserted  for  the 
purpose  of  reference  : — 

Symbols  and  Atomic  Weights  of  Elementary  Substances. 


Name 

Symbol  ; 

Atm.wt.  | 

Aluminium 

Al 

27-5 

Antimony 

Sb 

122- 

Arsenic    . 

As 

75' 

Barium    . 

Ba 

137* 

Bismuth  . 

Bi 

210- 

Boron 

B 

10-9 

Bromine  . 

Br 

80- 

Cadmium 

Cd 

112- 

Caesium  . 

Cs 

133- 

Calcium  . 

Ca 

40-        I 

Carbon    . 

C 

12' 

Cerium    . 

Ce 

92' 

Chlorine  . 

Cl 

35'5 

Chromium 

Cr 

5-'5 

i  Cobalt     . 

Co 

59' 

Name 

Symbol  jAtm.Wt. 

• 

Copper    . 

Cu            63-5 

Didymium 

D       j     96- 

Erbium    . 

Fluorine  . 

F            19- 

Glucinum 

G 

9'3 

Gold 

Au 

196-6 

Hydrogen 

H 

I  • 

Indium    . 

In 

1  13'4 

Iodine 

I 

127- 

i    Indium    . 

Ir 

197- 

,    Iron 

Fe 

56- 

Lanthanum 

La 

92- 

Lead 

Pb        207- 

1    Lithium  . 

L         r 

:    Magnesium 

Mg         24-3  j 

Equivalency  of  Electro-  Chemical  Action.         43 


Symbols  and  Atomic  Weights  of  Elementary  Substances — continued. 


Name 

Symbol 

Atm.  Wt. 

Name 

Symbol 

; 
Atm.  Wt. 

Manganese 

Mn 

55' 

Silver      . 

Ag 

108- 

Mercury  . 

Hg 

200' 

Sodium    . 

Na 

23- 

Molybdenum    . 

Mo 

96' 

Strontium 

Sr 

87-5 

Nickel     . 

Ni 

59- 

Sulphur  . 

S 

32- 

Niobium. 

Nb 

97'5 

Tantalum 

Ta 

I38- 

Nitrogen           . 

N 

H- 

Tellurium 

Te 

129- 

Osmium  , 

Os 

199' 

Thallium 

Tl 

204- 

Oxygen    . 

O 

16- 

Thorinum 

Th 

119' 

Palladium         , 

Pd 

106-5 

Tin 

Sn 

118- 

Phosphorus 

P 

31' 

Titanium 

Ti 

5°' 

Platinum 

Pt 

197- 

Tungsten 

W 

184* 

Potassium 

K 

Uranium 

U 

120' 

!   Rhodium           , 

Ro 

104-3 

Vanadium 

V 

137- 

Rubidium         . 

Rb 

85- 

Yttrium  . 

Y 

Ruthenium 

Ru    ' 

104-2 

Zinc 

Zn 

65- 

Selenium 

Se 

79-5 

Zirconium 

Zr 

895 

!  Silicon     . 

Si 

28- 

As  a  monad  exerts  one  equivalent  of  chemical  force,  a 
dyad  two,  a  triad  three,  &c.,  and  the  elementary  substances 
set  free  at  the  two  electrodes  are  liberated  in  their  chemically 
equivalent  proportions,  it  follows  chat  when  compounds  are 
decomposed  by  an  electric  current,  for  each  atomic  weight 
of  a  dyad  set  free  at  one  electrode,  two  of  a  monad,  or  one 
of  a  dyad,  are  liberated  at  the  other  ;  similarly  when  an 
atomic  weight  of  a  triad  is  separated  at  one  pole,  three  of  a 
monad,  or  one  and  a  half  of  a  dyad,  are  separated  at  the 
other,  and  so  on  ;  for  instance,  in  the  electrolysis  of  strong 
hydrochloric  acid,  one  part  by  weight  of  hydrogen  is  set 
free  at  the  cathode,  and  thirty- five  and  a  half  parts  of 
chlorine  at  the  anode.  In  the  electrolysis  of  water  two 
p.irts  by  weight  of  hydrogen  appear  at  the  cathode  and 
sixteen  parts  of  oxygen  at  the  anode,  and  so  on. 

Frequently,  however,  the  substances  which  are  set  free, 
or  appear  at  the  electrodes,  are  not  simple  elements,  but 
compound  bodies,  and  even  mixtures  of  compounds ;  but  in 
these  cases  also  a  similar  principle  of  chemical  equivalency 


44  The  A  rt  of  Electro-Metallurgy. 

operates,  and  we  may  say  generally,  whatever  substance,  or 
mixture  of  substances •,  are  set  free  at  one  electrode,  a  chemically 
equivalent  weight  of  substances  of  opposite  electrical  nature  is 
set  free  at  the  other. 

Definite  electro-chemical  action. — Not  only  are  the  element- 
ary and  compound  substances  which  are  set  free  at  the  two 
electrodes,  by  the  electrolysis  of  a  given  liquid,  liberated  in 
definite  proportions  by  weight,  which  are  identical  with  their 
chemically  combining  or  equivalent  proportions,  but  also,  if 
the  same  current  is  made  to  traverse  a  series  of  different 
liquids,  the  chemical  actions  in  all  of  them  are  also  in  chem- 
ically equivalent  quantities ;  and  therefore  produced  by  the 
same  amount  of  electricity.  This  great  truth  was  discovered 
by  Faraday. 

The  same  amount  of  electricity  which  will  decompose 
one  molecule  or  eighteen  parts  of  water,  setting  free  two 
parts  by  weight  of  hydrogen  and  sixteen  parts  of  oxygen  in 
one  vessel,  will  decompose  two  molecules  or  seventy-three 
parts  of  hydrochloric  acid,  setting  free  two  parts  of  hy- 
drogen and  seventy-one  parts  of  chlorine  in  another.  If 
we  cause  the  same  current  to  pass  through  a  solution 
of  cyanide  of  silver  and  potassium,  then  through  one  of 
sulphate  of  copper,  and  finally  through  one  of  antimony, 
each  solution  being  prepared  and  acted  upon  so  as  to  yield 
only  pure  metal,  we  find  that  for  every  108  parts  of  silver 

deposited  in  the  first  vessel,  3 175  parts  (or  .A5^  of  copper 

are  set  free  in  the  second  one  ;  and  40*66  parts  /'or  -  -  j 

of  antimony  in  the  third  one. 

By  employing  this  method  of  passing  the  same  current 
or  amount  of  electricity  through  successive  solutions,  and 
weighing  the  products  set  free,  their  relative  chemical  equiva- 
lents may  be  found  :  for  instance,  I  passed  a  voltaic  current 
through  a  solution  which  deposited  pure  copper  only,  and 
through  another  which  deposited  pure  antimony  alone,  ancj 


TJicory  cf  Electrolysis.  45 

weighed  the  amounts  of  deposit.  The  weight  of  the  copper 
obtained  was  317  grains,  and  of  the  antimony  40-6  grains, 
which  is  equal  to  one  atomic,  weight  or  63-5  parts  of  copper, 
as  the  equivalent  of  81*32  parts  of  antimony,  or  two-thirds 
an  atomic  weight  of  that  metals  12 1*98  as  the  full  atomic 
weight  of  antimony. 

Theory  of  electrolysis. — Faraday  considered  that  elec- 
trolytic decomposition  is  the  result  of  a  peculiar  corpuscular 
action  developed  in  the  direction  of  the  current ;  it  proceeds 
from  a  force  which  is  either  added  to  the  affinity  of  the  bodies' 
presenter  determines  the  direction  of  that  force.  The  elec- 
trolyte is  a  mass  of  acting  particles,  of  which  all  that  are  in 
the  course  of  the  current  contribute  to  the  terminal  action  ; 
and  in  consequence  of  the  affinity  between  the  elements 
being  weakened  or  partially  neutralised  by  the  current 
parallel  to  its  own  course  in  one  direction,  and  strengthened 
and  assisted  in  the  other,  the  combined  particles  acquire  a 
tendency  to  move  in  different  directions.  The  particles  of 
one  element,  a,  cannot  travel  from  one  pole  to  the  other  un- 
less they  meet  with  particles  of  an  opposed  substance,  b,  ready 
to  move  in  the  opposite  direction.  For  in  consequence  of 
their  increased  affinity  for  these  particles,  and  the  diminu- 
tion of  their  affinity  for  those  which  they  have  left  behind 
them  in  their  way,  they  are  continually  driven  forward. 

In  addition  to  the  law  of  definite  electro-chemical  action 
Faraday  has  advanced  what  is  termed  the  binary  theory  of 
electrolysis— that 'only  those  compounds  of  the  first  order 
are  directly  decomposable  by  the  electric  current,  which  con- 
tain one  atom  of  one  of  their  elements  for  each  atom  of  the 
other  ;  for  instance,  compounds  containing  one  atom  of  hy- 
drogen or  metal  with  one  atom  of  oxygen,  iodine,  bromine, 
chlorine,  fluorine,  or  cyanogen,'  whilst  '  boracic  anhydride 
(BO3),  sulphurous  anhydride  (SO2),  sulphuric  anhydride 
(SO3),  iodide  of  sulphur,  chloride  of  phosphorus  (PC13) 
and  (PCI 5),  chloride  of  sulphur  (S.,C1),  chloride  of  carbon 
(C4C16),  tetrachloride  of  tin  (SnCl4),  terchloride  of  arsenic 


46  The  A  rt  of  Electro-Metallurgy. 

(AsCl3),  pentachloride  of  antimony  (SbCl5)/  are  non-con- 
ductors of  electricity,  and  incapable  of  electrolysis. 

Secondary  effects  of  electrolysis. — Very  frequently  the  sub- 
stances which  appear  at  the  electrodes  are  not  those  ori- 
ginally set  free,  but  are  liberated,  or  set  free,  by  the  action  of 
the  originally  liberated  bodies  upon  the  liquid  or  upon  the 
electrode.  Some  substances  which  are  not  of  the  simple 
binary  character  mentioned  are  decomposed  by  current 
electricity,  and  yield  their  positive  and  negative  elements  in 
equivalent  proportions  at  their  respective  electrodes  ;  but 
according  to  this  theory  they  are  indirectly  decomposed,  i.e. 
they  are  decomposed  by  the  chemical  action  of  some  of 
the  elements  set  free  by  the  direct  action  of  the  current  upon 
other  substances  present.  For  instance,  'fused  borax 
(biborate  of  soda  Na2O,  2BO3)  yields  oxygen  gas  at  the 
anode  and  boron  at  the  cathode  ;  now,  since  fused  boracic 
acid  is  not  decomposed  by  the  electric  current,  the  separation 
of  the  boron  must  be  attributed  to  indirect  action ;  the  cur- 
rent resolves  the  soda  (Na2O)  into  oxygen  and  sodium,  and 
the  latter  separates  boron  from  the  boracic  acid  ;  (Faraday). 
In  a  similar  way  a  solution  of  common  salt  yields  chlorine 
at  the  anode,  and  hydrogen  and  soda  at  the  cathode. 
The  salt  is  probably  first  decomposed  into  chlorine  and 
sodium,  and  the  liberated  sodium  decomposes  the  water, 
forming  soda  and  setting  free  hydrogen,  for  when  the  cathode 
consists  of  mercuiy,  an  amalgam  of  sodium  is  obtained.  In 
other  cases,  as  that  of  a  solution  of  sulphate  of  copper,  nitrate 
of  silver,  or  chloride  of  gold,  the  hydrogen  produced  by  the 
decomposition  of  the  water  deoxidises  the  metallic  salts  in 
solution,  setting  free  their  metals  and  reconstituting  water. 
Similar  secondary  actions  take  place  at  the  anode  ;  if  that  elec- 
trode is  formed  of  an  easily  corrodible  metal  the  elements  -set 
free  at  its  surface  combine  with  it,  and  form  a  new  compound. 
In  other  cases  where  the  electrode  is  not  corroded,  as  an 
anode  of  platinum  in  a  solution  of  nitrate  of  silver  or  acetate 
of  lead,  the  liberated  oxygen  sometimes  converts  the  salt  into 


A  Hoy  of  Electro-Deposits  witJi  Electrode.        47 

an  insoluble  peroxide,  which  adheres  to  the  anode.  Second- 
ary effects  at  the  anode  may  sometimes  be  avoided  by  the 
employment  of  an  anode  of  platinum  or  gas-carbon. 

Alloy  of  deposits  with  the  cathode  and  with  each  other. — 
When  a  perfectly  clean  surface  of  a  metal  receives  a  deposit 
by  electrolysis,  in  the  great  majority  of  cases,  the  first  portions 
of  the  metal  deposited  penetrate  into  the  receiving  surface, 
and  form  either  a  mixture  or  alloy.  I  have  met  with  some 
new  instances  of  this  kind.  I  deposited  a  thick  coating  of 
copper  on  the  outside  of  a  platinum  cup.  After  heating  this 
cup  to  low  redness  a  few  times,  the  coating  became  loose, 
and  I  tore  it  all  off  and  digested  the  platinum  surface  in 
nitric  acid,  and  washed  it ;  it  then  looked  perfectly  free  from 
copper.  On  heating  it  again  to  low  redness  its  surface  became 
black  with  oxide  of  copper.  I  cleaned  it  again  in  a  similar 
manner  and  heated  it  once  more ;  the  surface  again  became 
black.  In  this  way,  even  after  cleaning  and  heating  six  or  eight 
times,  copper  appeared ;  the  copper,  therefore,  must  have 
passed  deeply  into  the  substance  of  the  platinum,  and  diffused 
again  outwards  in  the  process  of  heating  In  another  in- 
stance a  piece  of  thick  platinum  foil,  upon  which  I  had  de- 
posited a  film  of  tellurium  in  dilute  chloride  of  tellarium,  with 
a  tellurium  anode  and  a  current  from  five  Smee's  cells,  was 
scraped  very  clean  from  the  deposit  and  heated  to  low  red- 
ness. An  easily-fusible  alloy  was  formed  upon  the  surface, 
and  was  oxidised  and  reduced  repeatedly  in  the  flame  of  a 
Bunsen's  burner,  as  if  the  tellurium  had  soaked  into  the 
platinum. 

Sonstadt  also  observed  that  a  platinum  crucible  which  had 
been  thinly  electro-gilded  lost  its  golden  appearance  by 
heating  to  a  moderate  redness,  by  the  gold  soaking  as  it 
were  into  the  platinum  (Weldon's  '  Register,'  No.  36,  July 
1863,  p.  498).  In  the  process  termed  'pyroplating'  also,  an 
electro -deposited  layer  of  gold  upon  steel  nearly  disappears  on 
heating  the  steel  article  ;  a  second  layer  behaves  similarly  but 
to  a  less  extent ;  a  third  does  not  disappear  at  all  (*  Chemical 


48  The  Art  of  Electro- Metallurgy. 

News,'  vol.  xxvi.,  p.  137).  The  first  films  of  one  metal  electro- 
deposited  upon  another  frequently  form  an  alloy,  even  with- 
out the  aid  of  heat  ;  for  instance,  films  of  zinc  or  cadmium 
deposited  upon  copper  impart  to  its  surface  a  yellow  colour, 
and  in  other  cases  similar  effects  probably  occur,  but  do  not 
happen  to  be  observable.  If  one  of  the  metals  happens  to 
be  a  liquid  or  a  gas  the  effect  is  often  more  perfect  ;  thus 
most  metals,  even  those  of  the  earths  and  alkalies,  when 
deposited  upon  mercury  are  absorbed  by  it  and  form 
amalgams  ;  hydrogen  also,  when  deposited  upon  palladium, 
iron,  and  the  surfaces  of  various  metals,  penetrates  deeply 
into  tnem,  and  alters  their  properties.  This  diffusive  action 
of  one  metal  within  another  operates  not  only  during  the 
process  of  deposition,  but  continues  afterwards  ;  thus  a  yellow 
film  of  alloy,  obtained  by  depositing  copper  upon  zinc  or 
cadmium,  disappears  in  a  few  weeks,  as  if  absorbed  by  the 
metallic  substratum.  This  formation  of  metallic  compounds 
takes  place  also,  and  even  more  completely,  when  two  metals 
are  simultaneously  electro-deposited.  In  this  way  the  less 
easily  reducible  metals,  such  as  nickel,  and  iron,  in  the 
electro-deposition  of  which  hydrogen  is  simultaneously  de- 
posited, are  very  liable  to  contain  hydrogen  ;  and  in  the 
case  of  nickel  this  enclosed  gas  is  said  to  sometimes  cause 
the  deposit  to  split  and  curl  up,  and  separate  in  brilliant 
films  (Sprague's  *  Electro- Metallurgy.'  p.  305).  In  the 
case  of  antimony,  especially  that  deposited  from  the  bromide 
and  iodide,  large  bubbles  of  gas  gradually  accumulate  upon 
the  surface  of  the  deposit,  and  the  deposited  metal  is  full  of 
them.  The  explosive  character  of  some  electro-deposits  is 
also  probably  due  to  absorbed  hydrogen.  I  have  been  in- 
formed that  zinc  which  had  been  electro-deposited  in  a  grey- 
black,  spongy  mass  upon  the  iron  plates  of  an  exhausted 
battery,  consisting  of  ten  pairs  of  zinc  and  iron  plates,  ex- 
ploded when  struck ;  but  I  several  times  attempted  with- 
out success  to  obtain  such  a  deposit.  Napier,  in  his  '  Electro- 
Metallurgy,'  5th  edition,  p.  182,  speaks  of  explosive  electro- 


Purity  of  Electro-Deposited  Metals.  49 

deposited  bismuth.  A  writer  in  Dingler's  *  Polytechnic 
Journal 'also  speaks  of  electro-deposits  of  rhodium  and  iridium 
exploding  when  struck  (*  Journal  of  the  Chemical  Society,' 
vol.  ii.,  p.  1007). 

The  absorption  of  electro-deposited  hydrogen  has  a  great 
effect  upon  the  properties  of  iron  and  steel.  *  If  after  im- 
mersion, say,  ten  minutes  in  either  sulphuric  or  hydrochloric 
acid,  a  piece  of  iron  or  steel  be  tested,  its  tensile  strength 
and  resistance  to  torsion  will  be  found  to  be  diminished. 
Exposure  to  the  air  for  several  days,  or  gentle  heat,  will 
however  restore  its  original  strength'  (W.  H.  Johnson, 
1  Chemical  News,' vol.  xxvii.,pp.  82  and  176;  also  vol.  xxix., 
pp.  89  and  213  ;  also  Professor  O.  Reynolds,  p.  118  of  the 
same  volume.  Compare  also  the  paragraphs  on  electro- 
deposition  of  hydrogen  and  its  absorption  by  deposited 
metals,  pp.  96,  247). 

As  steam  boilers  are  occasionally  supplied  with  water 
containing  traces  of  acids,  and  the  degree  of  acidity  of  the 
water  becomes  stronger  by  the  evolution  of  steam,  it  is 
reasonable  to  suppose  that  the  deposition  of  hydrogen  by  the 
simple  immersion  process,  and  its  absorption  by  the  iron, 
may  in  some  cases  contribute  to  the  bursting  of  those 
vessels ;  and  in  such  cases  the  electro-deposition  of  hydrogen 
is  a  circumstance  not  to  be  neglected. 

Purity  of  electro-deposited  metals.. — Electro-deposited 
metals  are  by  no  means  necessarily  pure  ;  they  rarely  are 
so,  and  the  reason,  probably,  why  the  popular  notion  has 
arisen  that  they  are  very  pure  is  because  copper  is  the 
metal  most  frequently  deposited,  and  such  copper  happens 
to  be  an  exceptional  instance  of  purity.  The  degree  of 
purity  of  deposited  metals  depends  chiefly  upon  the  degree 
of  purity  of  the  solution  ;  if  that  is  pure  the  deposit  is  likely 
to  be  so,  and  will  be  so  unless  it  unites  with  the  hydrogen 
liberated  simultaneously  with  it,  or  with  any  of  the  constitu- 
ents of  the  liquid,  as  in  the  instance  of  amorphous  or  *  ex- 
plosive antimony.'  The  purity  of  the  solution  largely  de- 


50  The  A  rt  of  Electro-Metallurgy. 

pends  upon  the  circumstance  whether  the  anode  is  pure,  and 
whether  its  impurities  are  soluble  in  the  liquid  ;  if  they  are 
not,  they  cannot  be  deposited  \  if  they  are  soluble,  then  their 
deposition  or  not  will  largely  depend  upon  the  circumstances 
.mentioned  in  the  immediately  following  and  preceding  para- 
graphs. The  great  purity  of  electro-deposited  copper  is 
largely  dependent  upon  the  fact  that  any  lead  contained  in 
the  anode  is  insoluble  in  a  sulphate  solution,  and  any  zinc 
contained  in  it  is  too  electro-positive  in  an  acid  solution  to 
be  thrown  down  with  the  copper. 

Electrolysis  of  mixed  liquids. — Of  the  electrolysis  of  mixed 
metallic  solutions  comparatively  little  is  known  ;  if,  however, 
a  solution  contains  several  dissolved  metals  of  very  different 
degrees  of  positive  electric  capacity,  the  least  positive  metal 
is  usually  deposited  first,  unless  there  is  an  insufficient 
amount  of  that  metal  present  to  convey  the  whole  of  the 
current ;  and  if  the  current  is  continued  till  the  whole  of  the 
metals  are  deposited,  the  most  positive  one  is  the  last  to  be 
liberated.  It  is  probable,  also,  that  if  the  metals  are  about 
equally  positive  in  the  particular  liquid,  and  their  salts  possess 
an  approximately  equal  degree  of  conducting  power,  and 
are  not  widely  different  in  quantity,  the  current  divides  itself 
between  them,  and  is  conducted  by  each  ;  but  much  investi- 
gation needs  to  be  made  in  this  part  of  the  subject. 

Electro-deposition  of  alloys. — It  is  much  more  difficult  to 
deposit  zinc  than  copper,  because  zinc  is  more  electro-posi- 
tive ;  it  is  still  more  difficult  to  deposit  two  metals  than  one, 
especially  if  one  of  the  metals  is  highly  electro-positive  to 
the  other,  as  zinc  usually  is  to  copper,  and  it  can  only  be 
effected  by  selecting  a  liquid  in  which  the  one  metal  is  but 
feebly  electro-positive  to  the  other.  According  to  the  late 
eminent  investigator,  Professor  Magnus,  the  separate  and 
simultaneous  deposition  of  substances  from  a  mixed  solution 
depends  :  ist,  on  the  density  of  the  current ;  2nd,  on  the 
proportions  in  which  the  different  substances  exist  in  the 
fluid  ;  3rd,  on  the  nature  of  the  electrodes  ;  and  4th,  on  the 


Electro-Deposition  of  Alloys.  51 

greater  or  less  facility  with  which  one  or  the  other  substance 
can  be  carried  from  stratum  to  stratum  within  the  fluid  ;  as 
well  as  on  the  obstacles  which  stand  in  the  way  of  this 
transmission,  either  in  the  shape  of  porous  walls  or  in  any 
other  form  (*  Philosophical  Magazine,'  4th  series,  vol.  xii., 

P-  iS9)- 

With  solutions  in  which  alloys  are  to  be  deposited  the 
most  important  condition  is,  that  neither  of  the  metals  to  be 
deposited  shall  be  electro-positive  to  the  other  in  that  liquid. 
This  is  best  tested  by  taking  a  wire  of  each  metal,  connecting 
them  with  a  galvanometer,  and  simultaneously  immersing 
their  free  ends  in  the  liquid  ;  if  either  is  electro-positive  the 
needle  of  the  instrument  will  be  deflected,  while  the  amount 
of  deflection  will  indicate  the  amount  of  their  electric  differ- 
ence in  that  liquid.  It  may  also  be  tested  by  immersing  a 
wire  of  each  metal  (not  in  mutual  contact)  in  the  liquid ;  if 
either  become  coated  with  the  other  metal  in  one  hour,  that 
one  is  positive ;  but  if  neither  becomes  coated  in  six  hours, 
there  is  probably  no  considerable  electric  difference  between 
them. 

The  following  experiments  of  mine  show  that  if  a  liquid 
contains  two  metals  in  solution,  and  a  wire  or  other  piece  of 
each  of  those  metals  is  immersed  in  the  liquid,  and  one 
becomes  coated  with  a  deposit  of  metal,  while  the  other  does 
not,  the  coated  one  is  electro -positive  to  the  other  in  that 
liquid,  and  the  solution  will  only  yield  by  means  of  a  feeble 
separate  current  the  same  metal  which  is  deposited  by  simple 
immersion. 

First  experiment. — With  an  alloy  solution,  consisting  of 
equal  measures  of  a  strong  solution  of  protochloride  of  tin, 
and  terchloride  of  antimony,  with  an  anode  either  of  tin  or 
of  antimony  (the  latter  is  the  more  suitable  because  it  does 
not  become  coated  by  simple  immersion  in  the  liquid),  a 
copper  cathode,  and  a  single  cell  of  small  Smee's  battery,  only 
antimony  was  deposited  ;  the  tin  became  coated  with  anti- 

£2 


5  2  The  A  rt  of  Electro- Metallurgy. 

mony  by  simple  immersion,  and  was  found  by  the  galvano- 
meter to  be  strongly  positive  to  that  metal. 

Second  experiment. — With  a  liquid  composed  of  equal 
measures  of  a  solution  of  protochloride  of  tin  and  chloride 
of  bismuth,  and  either  a  bismuth  or  tin  anode  (the  former 
is  the  best),  a  brass  cathode,  and  a  small  single  cell  of 
Smee's  battery,  only  bismuth  was  found  to  be  deposited  ;  the 
tin  was  positive  to  the  bismuth  by  the  galvanometer,  and 
became  coated  quickly  with  that  metal  by  simple  immersion. 

Third  experiment. — With  a  mixture  of  equal  measures 
of  terchloride  of  antimony  and  chloride  of  bismuth,  antimony 
anode,  copper  cathode,  and  a  feeble  Smee's  battery,  only 
antimony  was  deposited;  bismuth  became  slowly  coated 
with  antimony  in  the  solution  by  simple  immersion,  and  was 
found  by  the  galvanometer  to  be  moderately  positive  to  the 
latter  metal  in  it. 

Fourth  experiment. — With  100  grains  each  of  proto- 
chloride of  tin  and  chloride  of  zinc  dissolved  together  in  an 
ou'nce  of  distilled  water,  tin  anode,  copper  cathode,  and  one 
small  Smee's  cell,  only  tin  was  deposited  ;  zinc  was  positive 
to  tin  in  this  liquid  by  the  galvanometer,  and  deposited  tin 
upon  itself  by  simple  immersion. 

Fifth  experiment. — With  equal  measures  of  strong  solu- 
tions of  nitrate  of  zinc,  and  ternitrate  of  bismuth,  and  a 
little  nitric  acid,  bismuth  anode,  copper  cathode,  and  a 
feeble  one-pair  battery,  only  bismuth  was  deposited  ;  zinc 
was  strongly  positive  to  bismuth  in  this  liquid  by  the  galva- 
nometer, and  became  quickly  coated  with  that  metal  by 
simple  immersion. 

Sixth  experiment. — With  a  solution  of  mixed  sulphates 
of  zinc  and  copper,  copper  anode  and  cathode,  and  a  single 
small  battery,  copper  alone  was  deposited  ;  zinc  was  strongly 
positive  to  copper  in  this  liquid  by  the  galvanometer,  and 
coated  itself  immediately  with  copper  in  it  by  simple 
immersion. 

Further,  if  we  take  some  distilled  water,  and  dissolve 


Electro-Deposition  of  Alloys.  53 

some  caustic  potash  in  it,  and  pass  a  moderately-strong 
current  through  it  by  platinum  electrodes,  hydrogen  gas 
will  alone  be  set  free  at  the  cathode ;  in  this  case  also 
the  least  positive  of  the  two  elements  of  the  liquid — potas- 
sium and  hydrogen — is  set  free  or  deposited.  If  we  now 
add  a  little  sulphuric  acid  to  the  solution  to  neutralise  and 
convert  it  into  a  solution  of  sulphate  of  potash,  add  some 
sulphate  of  zinc  besides,  and  pass  a  weak  current  through 
the  liquid,  we  shall  obtain  a  deposit  of  zinc  on  the  cathode, 
but  no  hydrogen  or  potassium.  In  this  case  we  cannot  de- 
termine by  the  galvanometer  which  is  the  most  positive  in 
this  liquid,  hydrogen  or  zinc,  because  the  former  is  a  gas  ; 
but  it  is  probable  that  hydrogen  is  most  positive,  because 
the  zinc  does  not  evolve  it  by  simple  immersion  in  this  liquid. 

If  we  further  add  to  the  liquid  a  small  quantity  of  sul- 
phate of  copper,  and  treat  it  as  before,  neither  potassium, 
hydrogen,  nor  zinc  will  be  deposited,  but  only  copper ;  we 
also  find  by  the  galvanometer  that  copper  is  less  positive  than 
zinc  in  such  a  liquid,  and  that  zinc  coats  itself  with  copper 
in  it  by  simple  immersion  ;  in  this  case  also  the  least  positive 
of  the  positive  elements  is  alone  deposited.  From  these  and 
many  other  experiments  which  I  have  made  with  similar 
results  we  deduce  the  following  rule  :— If  a  liquid  contains 
several  metals  or  electro- positive  substances,  and  a  weak 
electric  current  is  passed  through  it,  only  that  substance 
which  is  the  least  electro-positive  will  be  deposited. 

With  regard  to  the  influence  exercised  by  the  proportions 
of  the  ingredients  of  the  liquid,  and  the  strength  of  the  cur- 
rent,  I  may  observe  that  if  the  liquid  contains  several  metal? 
dissolved  in  equal  quantities,  and  only  one  is  being  deposited 
by  the  passage  of  a  weak  current,  a  considerable  increase  in 
the  strength  of  current  will  cause  a  portion  of  the  next  more 
positive  metal  to  be  deposited  along  with  the  less  positive 
one  ;  but  this  alloy  deposit  will  not  be  very  coherent,  because 
the  power  required  to  deposit  the  second  metal  in  the  regu- 
line  state  will  be  so  great  as  to  deposit  the  first  as  a  soft 


5  4  The  A  rt  of  Electro- Metallurgy. 

powder  ;  and  this  holds  most  true  when  the  difference  of  elec- 
tric power  required  is  the  greatest.  Thus,  ist,  if  small  quan- 
tities of  sulphate  of  zinc  and  sulphate  of  copper  are  dissolved 
together  in  a  large  quantity  of  water,  and  a  feeble  current 
passed  through  the  solution,  only  reguline  copper  will  be 
deposited;  but  if  the  current  passing  be  considerably  in- 
creased, the  deposit  of  copper  will  cease  to  be  reguline,  and 
zinc  will  be  deposited  with  it.  If  the  power  be  still  further 
increased,  hydrogen  gas  will  also  be  evolved  at  the  surface 
of  the  deposited  metals.  2nd,  if  we  dissolve  a  small  quan- 
tity of  sulphate  of  copper  and  a  large  quantity  of  sulphate  of 
zinc  in  a  large  quantity  of  water,  and  pass  a  strong  current 
through  the  solution,  copper,  zinc,  and  hydrogen  will  be  set 
free  at  the  cathode.  3rd,  if  we  slightly  moisten  a  lump  of 
caustic  potash  with  pure  water,  and  pass  a  weak  current 
through  it  by  platinum  electrodes,  hydrogen  alone  will  be  set 
free  at  the  cathode  ;  but  if  a  very  powerful  current  is  em- 
ployed, potassium  also  will  be  deposited.  In  each  of  these 
cases  we  find  that  when  the  current  is  least  dense  the  least 
positive  of  the  positive  substances  is  alone  deposited  ;  but 
if  the  power  is  sufficiently  increased,  and  there  is  only  a  small 
portion  of  the  less  positive  substance  present,  the  more  po- 
sitive substances,  even  though  they  are  much  more  positive, 
will  also  be  deposited.  The  weaker  affinities  are  overcome 
first  and  to  the  greatest  extent ;  the  current  of  electricity  ex- 
ercising its  influence  first,  and  in  the  greatest  proportions, 
upon  the  salt  of  the  least  positive  metal. 

Polarisation  of  electrodes. — After  an  electric  current  has 
been  passing  for  some  time  between  two  electrodes  in  a 
liquid,  if  the  electrodes  be  separated  from  the  source  of  the 
current,  and  whilst  they  remain  undisturbed  in  the  liquid  be 
connected  with  a  galvanometer,  a  current  occurs,  and  in  a 
reverse  direction  to  that  of  the  original  one.  It  often  also 
occurs,  but  to  a  less  extent,  if  the  two  electrodes  are  trans- 
ferred to  another  liquid,  or  if  two  fresh  electrodes  are  care- 
fully immersed  in  the  corresponding  parts  of  the  same  liquid. 


Peroxides  on  Anodes.     Electrolytic  Movements.     55 

This  phenomenon,  known  as  a  '  polarisation/  continually 
occurs  in  electro-metallurgical  processes,  and  may  be  ex- 
plained as  follows  : — the  various  substances,  either  primarily 
liberated,  or  secondarily  formed,  at  the  two  electrodes,  either 
adhere  in  a  solid  state  to  the  electrodes,  or  fall  to  the 
bottom,  or  dissolve  in  the  liquid,  or  escape  as  gas  ;  but  in 
either  case  they  more  or  less  accumulate  about  the  electrodes, 
adhere  to,  or  are  absorbed  by  them,  and  alter  their  electrical 
relations.  The  direction  of  the  current  produced  by  polar- 
isation is  opposite  to  that  of  the  original  one,  because  the 
latter  has  liberated  electro-negative  substances  at  the  positive 
pole,  and  positive  substances  at  the  negative  pole. 

Formation  of  peroxides  upon  the  anode. — Solutions  of  some 
metals,  when  electrolysed  with  platinum  electrodes,  are  spe- 
cially liable  to  form  layers  of  insoluble  peroxide  upon  the 
anodes  by  the  action  of  the  free  oxygen  of  the  water,  liberated 
there  by  electrolysis.  This  is  the  case  with  those  of  the 
nitrates  of  lead,  silver,  and  bismuth,- the  nitrate  and  acetate 
of  manganese,  and  alkaline  solutions  of  lead,  cobalt  and 
nickel  (See  *  Journal  of  the  Chemical  Society/  vol.  ix.,  p.  307). 
In  preparing  the  peroxides  of  bismuth,  lead,  nickel,  cobalt, 
and  manganese,  by  this  method,  very  weak  electric  currents 
must  be  used.  That  of  cobalt  is  readily  prepared,  and  is 
permanent;  its  colours  are  magnificent,  and  may  find  an 
industrial  use  in  the  art  of  metallo-chromy  (See  pp.  242, 
260  ;  Wernicke,  '  Chemical  News/  vol.  xxii.,  p.  240). 

Movements  in  electrolytes. — As  incidental  effects  of  elec- 
trolysis I  may  mention  the  movements  which  take  place  in 
depositing  liquids  during  the  passage  of  the  current.  In 
nearly  all  cases  the  layer  of  liquid  in  contact  with  the  anode, 
by  dissolving  a  portion  of  that  body,  becomes  specifically 
heavier  than  the  remainder  of  the  solution,  and  gradually 
sinks  to  the  bottom ;  whilst  that  in  contact  with  the  cathode, 
by  abstraction  of  its  metal,  suffers  a  reverse  change;  i.e.  it 
becomes  specifically  lighter  and  rises  to  the  top.  In  this  way 
a  layer  of  heavier  liquid  accumulates  at  the  bottom  of  the 


5  6  The  A  rt  of  Electro-Metallurgy. 

vessel,  and  one  of  less  specific  gravity  collects  at  the 
surface.  At  the  same  time  these  two  layers  slowly  dif- 
fuse into  the  intervening  strata  of  the  liquid,  and  thus  the 
whole  solution  tends  to  become  uniform ;  but  if  this  process 
of  diffusion  is  less  rapid  than  that  of  separation,  there  is  a 
constant  state  of  difference  of  chemical  composition  and  of 
specific  gravity  maintained  between  the  upper  and  lower 
parts  of  the  liquid.  Certain  effects  result  from  this,  viz.,  the 
anode  corrodes  away  very  freely  at  its  upper  part,  the  cathode 
receives  a  rapid  and  thick  deposit  at  its  lower  part ;  the 
current  traverses  the  liquid  in  an  oblique  direction  down- 
wards ;  the  anode  does  not  dissolve  at  its  lower  portion, 
and  the  upper  end  of  the  cathode  receives  no  deposit.  And 
if  the  liquid  is  very  dense,  and  contains  much  free  acid,  each 
electrode  behaves  like  a  single  metal  immersed  vertically  in 
two  liquids  (see  p.  84),  and  generates  a  current  between  its 
upper  and  lower  parts  independently  of  the  one  which  comes 
from  the  battery  ;  this  independent  current  at  the  anode  dis- 
solves the  upper  portion  of  that  body,  and  produces  a  metallic 
deposit  upon  its  lower  end,  and  the  one  at  the  cathode 
produces  similar  effects  upon  that  metal ;  and  thus  a  deposit 
upon  the  upper  end  of  a  cathode  may  actually  redissolve  and 
disappear  even  whilst  the  battery  current  is  passing.  The 
most  effectual  way  of  counteracting  these  effects  is  to  have 
the  solution  sufficiently  dilute,  without  an  excess  of  free  acid 
or  other  solvent,  to  electrolyse  it  with  moderate  speed,  and 
to  stir  it  continually,  or  keep  the  electrodes  in  motion. 

Magneto-electric  action. — Electro-chemical  and  chemico- 
electric  actions,  together  with  the  principles  and  laws  which 
regulate  them,  constitute  the  essential  part  of  the  basis  of 
electro-metallurgy  ;  magneto-electric  action  is  only  a  subsi- 
diary subject,  because  magneto-electric  machines  are  merely 
one  of  the  sources  which  may  be  employed  of  the  electric 
current  used  in  the  art,  and  forms  no  part  of  the  process 
it?elf.  As  also  the  principles  of  magneto-electric  induction, 
and  the  construction  and  action  of  magneto- electric  ma- 


Magneto-Electric  Action.  57 

chines,  are  already  described  in  the  treatise  on  <  Electricity 
and  Magnetism '  (pp.  70  and  280)  in  this  Series,  it  is  unneces- 
sary for  me  to  say  more  than  a  few  words  on  this  part  of 
the  subject. 

Strictly  speaking,  magneto- electric  action  should  be 
termed  mechanico-electric  action,  because  mechanical  power 
is  the  cause  and  electricity  the  effect,  and  the  magnetism 
acts  only  as  an  intermediate  agent,  by  means  of  which  the 
mechanical  energy  is  enabled  to  produce  or  be  transformed 
into  electricity.  The  fundamental  fact  or  principle  of  mag- 
neto-electric action  is,  wherever  there  is  varying  magnetism, 
there  is  an  electric  current  induced  in  an  adjacent  closed 
conducting  circuit  at  right- angles  to  it. 

Magnetism  in  the  vicinity  of  a  conductor  of  electricity 
may  be  caused  to  vary  by  several  means,  viz.  by  heating  or 
cooling  the  magnetised  body  (I  have  employed  this  method, 
'Proceedings  of  the  Royal  Society/  1869,  No.  108),  by 
otherwise  changing  the  strength  of  .the  magnet,  by  altering 
the  distance  of  the  magnet  from  the  conductor,  or  by  vary- 
ing their  relative  positions  to  each  other.  The  first  of  these 
methods  is  rarely  used,  because  it  is  not  convenient ;  but 
the  others  are  commonly  employed,  and  are  very  suitable 
and  effective.  The  current  lasts  only  during  the  increase 
or  decrease  of  the  magnetism,  and  is  reverse  in  direction  in 
the  two  cases,  as  indicated  in  the  annexed  figures  12  and  13. 

The  magnetism  acting  upon  the  conductor  may  be  in- 
creased or  decreased,  by  alternately  approaching  the  magnet 
towards  and  withdrawing  it  from  the  conductor,  or  by  al- 
ternately magnetising  and  demagnetising  a  bar  of  soft  iron, 
upon  which  the  conductor  is  wound ;  the  latter  is  the 
method  generally  employed,  and  is  usually  effected  by  rotat- 
ing the  iron  bar  and  its  surrounding  conductor  between  the 
poles  of  a  magnet. 

The  alternate  currents  produced  in  th*»  surrounding  con- 
ductor by  the  magnetisation  and  demagnetisation  of  the 
iron  are  opposite  in  direction,  and  are  caught  up  and  thrown 


5  8  The  A  rt  of  Electro-Metallurgy. 

into  one  uniform  course  by  means  of  a  mechanical  arrange- 
ment termed  a  commutator,  which  is  fixed  to  the  iron  arma- 


FlG.  12. 


Increasing  magnetism. 
FIG.  13. 


Decreasing  magnetism. 

ture  and  revolves  with  it.  The  current,  therefore,  usually 
obtained  by  magneto-electric  action  differs  from  that  result- 
ing from  a  chemico-electric  source,  in  being  a  succession  of 
momentary  streams  of  electricity,  all  flowing  in  the  same 
direction. 

Mr.  Henry  Wilde,  of  Manchester,  discovered  that  if  the 
current  from  the  wire  of  the  revolving  armature  was  made 
to  flow  through  a  coil  of  insulated  wire  surrounding  a  large 
bar  of  soft  iron,  a  degree  of  magnetism  many  times  stronger 
than  that  of  the  original  magnet  might  be  produced  by  re- 
volving the  armature  sufficiently  fast ;  and  that  by  an  exten- 
sion of  this  principle  of  accumulation,  magnets  of  any  degree 
of  power  might  be  obtained,  limited  only  by  the  capacity  of 
the  iron  to  receive  magnetism,  and  the  amount  of  mechan- 
ical power  expended  in  rotating  the  armatures. 

In  all  magneto-electric  machines  there  exists,  during  their 


Thermo-Electric  Action.  59 

continuance  of  action,  incessant  molecular  vibrations  in  the 
magnet  and  armature,  caused  by  the  changes  of  magnetism, 
and  in  the  conducting-wires,  caused  by  the  electrical  waves  ; 
and  in  consequence  of  these  vibrations  considerable  heat 
is  produced,  which  differs  in  amount  in  different  machines. 
In  this  way  a  portion  of  the  mechanical  power  expended  is 
converted  into  heat  instead  of  into  electricity  ;  and,  in  ad- 
dition to  this,  the  heat  is  liable  to  injure  the  insulation  of  the 
wires  upon  the  armature,  and  damage  the  bearings  of  the 
revolving  parts  of  the  machine. 

The  kinds  of  magneto- electric  machines  employed  for 
electro-deposition,  together  with  additional  information  of  a 
more  technical  kind,  will  be  illustrated  and  given  in  the 
practical  division  (p.  345)  of  this  book. 

Thermo-electric  action. — Thermo-electric  action  is  a  much 
more  secondary  matter  at  present  than  magneto- electric 
induction  in  relation  to  electro-metallurgy,  because  it  is  as 
yet  but  little  used  in  the  art ;  but  its  use  will  probably  be 
largely  extended,  and  may  even  supersede  that  of  magneto- 
electric  induction,  because  it  is  a  much  more  direct  conver- 
sion of  heat  into  electric  force. 

The  chief  fact  of  thermo-electric  action  was  discovered 
by  Seebeck  in  1823,  and  is  as  follows:  If  we  take  two  bars, 
A  and  B  (see  Fig.  14),  of  any  two  metals,  especially  bis-, 
muth  and  antimony,  solder  their  junctions,  connect  their 
free  ends  by  wires,  and  apply  heat  to  the  soldered  junction, 

FIG.  14. 


C-- — —     < 
13  isTtiutk                                  Ajtttf  monjr  J 

Cold  — *B  Hot  -A—*  Cold 

a  portion  of  the  applied  heat  is  absorbed  and  disappears, 
and  an  electric  current  is  produced  in  its  stead. 

All  metals  and  other  conductors  of  electricity  are  capable 


6o 


The  A  rt  of  Electro-Metallurgy. 


of  producing  the  current,  and  they  are  usually  classed  into 
thermo-electro-positive,  or  those  in  which  the  current  pro- 
ceeds from  the  colder  to  the  warmer  portion,  as  with  bismuth; 
and  thermo-electro-negative,  or  those  in  which  it  proceeds 
in  the  reverse  direction,  as  with  antimony. 

In  the  following  table  by  Dr.  Mattheissen,  the  various 
metals,  &c.,  are  arranged  in  a  series  according  to  their  relative 
degrees  of  thermo-electric  tension  : — 

Thermo-electro-positive. 

Bismuth,  commercial  +     .  97'  Cobalt          .  .  .22- 

,,         pure       .  .  89*  German-silver  .  .11*75 

,,         crystal  axial        .  65*  Mercury        .  .  .        -418 

„  ,,     equatorial  45-  Lead    ,         .  .          Neutral 

Thermo-electro-negative. 


Arsenic 

Iron,  pianoforte  wire     . 
Antimony,  crystal  axial 
„  „     equa- 

torial 

Red  phosphorus   . 
Tellurium     . 
Selenium 


i7'5 

22-6 

26-4 
502- 


Copper,  commercial          .  *l 

Platinum          ...  "9 
Gold        .         .         .        .1-2 

Antimony,  pressed  wire    .  2*8 

Silver,  pure  and  hard        .  3' 

Zinc,  pure,   pressed  wire  3-7 

Copper,  electro-deposited  3-8 
Antimony,       commercial, 

pressed  wire        .         .  6* 

Not  only  solid  conductors  of  electricity,  but  also  liquid 
ones,  are  capable  of  yielding  thermo-electric  currents,  and 
I  have  devised  and  employed,  in  several  researches  on  the 
subject,  various  apparatus  for  the  purpose  ('  Philosophical 
Magazine,'  January  1857; '  Proceedings  of  the  Royal  Society,' 
1871  ;  Watt's  Dictionary,  2nd  Supplement,  p.  457). 

The  kinds  of  thermo-electric  apparatus  which  have  as  yet 
been  employed  in  electro-metallurgy  are  described  in  the 
special  practical  section  of  this  book  (p.  349). 


CHEMICAL  PRINCIPLES  OF  ELECTRO-METALLURGY. 

Chemico-electric  relations  of  substances.— Chemico-electric 
action  often  takes  place  in  electro-metallurgical  processes ;  it 


Chemico -Electric  Series.  6 1 

continually  occurs  in  the  voltaic-batteries  whilst  they  are  in 
use  ;  it  also  takes  place  under  several  circumstances  when 
metals  are  immersed  in  conducting  liquids  ;  for  instance, 
it  occurs  when  any  metal  is  immersed  in  an  acid  solution 
of  a  less  positive  metal  than  itself,  as  when  steel  or  iron 
is  dipped  into  a  solution  of  sulphate  of  copper,  a  portion 
of  the  steel  or  iron  dissolves,  and  produces  an  electric 
current.  The  importance  of  a  knowledge  of  the  relation  of 
chemico-electric  action  to  electro-metallurgy  may  be  shewn  by 
the  fact,  that  any  liquid,  say  the  one  just  mentioned,  in 
which  the  metal  to  be  coated,  say  iron,  is  strongly  electro- 
positive to  the  metal  in  solution,  and  with  which  it  is  in- 
tended to  be  coated,  is  usually  unfit  to  be  used  for  coating 
that  particular  metal,  because  if  a  thick  coating  is  formed 
upon  it  the  deposit  will  not  adhere  firmly. 

Chemico- electric  series. — The  following  table  exhibits  the 
usual  relative  electrical  positions  to  each  other  in  most 
liquids  of  a  number  of  the  elementary  substances  ;  the  first 
substance  named  being  the  most  electro-positive,  and  the 
last  one  the  most  electro-negative  : — 

Potassium  +  Copper  Phosphorus 

Sodium  Silver  Selenium 

Magnesium  Mercury  Iodine 

Zinc  Platinum  Bromine 

Iron  Gold  Chlorine 

Aluminium  Hydrogen  Nitrogen 

Lead  Antimony  Sulphur 

Tin  Carbon  Fluorine 

Bismuth  Tellurium  Oxygen— 

In  this  series  every  substance  is  usually  positive  to  all 
those  below  it,  and  negative  to  those  above ;  consequently 
none  are  absolutely  positive  or  negative,  and  therefore  the 
series  cannot  strictly  be  divided  into  two  classes,  one  con- 
sisting wholly  of  positive  and  the  other  of  negative  bodies; 
but  it  is  usual,  nevertheless,  to  speak  of  the  metals,  especially 
the  alkali  and  base  metals,  as  positive,  and  the  metalloids  as 


62 


The  Art  of  Electro-Metallurgy. 


negative  substances.  Many  exceptions  might  be  shewn  with 
regard  to  the  positions  of  the  substances  in  the  above  series, 
because  the  order  varies  with  every  different  liquid  in  which 
they  may  be  immersed,  and  therefore  the  table  is  only  of 
value  for  usual  guidance. 

Electrical  relations  of  metals  in  liquids. — There  are  several 
arrangements  of  immersing  metals  in  liquids,  by  means  of 
which  electric  currents  are  produced,  and  they  may  be  classed 
as  follows  :  i.  By  the  immersion  of  two  metals  in  one  liquid. 
2.  Of  one  metal  in  two  liquids.  3.  Of  two  metals  in  two 
liquids,  &c. 

i.  By  the  immersion  of  two  metals  in  one  liquid. — If  we 
connect  two  pieces,  A  and  B,  of  different  kinds  of  metal  with 
the  two  ends  of  the  coil  of  a  galvanometer  C  (see  Fig.  15),  and 

Fig.  15- 


immerse  them  in  a  conducting  liquid,  D,  an  electric  current  is 
generated  by  chemical  action,  and  the  needle  is  deflected  ; 
and  if  we  examine  the  behaviour  of  a  number  of  metals  thus 
in  a  variety  of  different  liquids,  and  arrange  them  in  series  ac- 
cording to  their  degrees  of  electrical  power,  we  find  that  the 
electrical  positions  of  the  metals  usually  agree  with  the  order 
given  in  the  foregoing  table  ;  and  we  also  find  that  their 
order  is  somewhat  different  in  every  different  liquid. 

The  electrical  orders  of  metals,  &c.,  in  a   number  of 


Chemico-Electric  Series.  6 1 

continually  occurs  in  the  voltaic-batteries  whilst  they  are  in 
use  ;  it  also  takes  place  under  several  circumstances  when 
metals  are  immersed  in  conducting  liquids  ;  for  instance, 
it  occurs  when  any  metal  is  immersed  in  an  acid  solution 
of  a  less  positive  metal  than  itself,  as  when  steel  or  iron 
is  dipped  into  a  solution  of  sulphate  of  copper,  a  portion 
of  the  steel  or  iron  dissolves,  and  produces  an  electric 
current.  The  importance  of  a  knowledge  of  the  relation  of 
chemico-electric  action  to  electro-metallurgy  may  be  shewn  by 
the  fact,  that  any  liquid,  say  the  one  just  mentioned,  in 
which  the  metal  to  be  coated,  say  iron,  is  strongly  electro- 
positive to  the  metal  in  solution,  and  with  which  it  is  in- 
tended to  be  coated,  is  usually  unfit  to  be  used  for  coating 
that  particular  metal,  because  if  a  thick  coating  is  formed 
upon  it  the  deposit  will  not  adhere  firmly. 

Chemico-electric  series. — The  following  table  exhibits  the 
usual  relative  electrical  positions  to  each  other  in  most 
liquids  of  a  number  of  the  elementary  substances  ;  the  first 
substance  named  being  the  most  electro-positive,  and  the 
last  one  the  most  electro-negative  : — 

Potassium  +  Copper  Phosphorus 

Sodium  Silver  Selenium 

Magnesium  Mercury  Iodine 

Zinc  Platinum  Bromine 

Iron  Gold  Chlorine 

Aluminium  Hydrogen  Nitrogen 

Lead  Antimony  Sulphur 

Tin  Carbon  Fluorine 

Bismuth  Tellurium  Oxygen  — 

In  this  series  every  substance  is  usually  positive  to  all 
those  below  it,  and  negative  to  those  above ;  consequently 
none  are  absolutely  positive  or  negative,  and  therefore  the 
series  cannot  strictly  be  divided  into  two  classes,  one  con- 
sisting wholly  of  positive  and  the  other  of  negative  bodies; 
but  it  is  usual,  nevertheless,  to  speak  of  the  metals,  especially 
the  alkali  and  base  metals,  as  positive,  and  the  metalloids  as 


64  The  A  rt  of  Electro-Metallurgy. 

5.  Hydrochloric  Acid  (Faraday). 

Zinc  +  Iron  Silver 

Cadmium  Copper  Antimony— 

Tin  Bismuth 

Lead  Nickel 

6.   I  volume  of  Nitric  Acid  and  7  volumes  of  Water  (Faraday). 
Zinc  +  Iron  Copper 

Cadmium  Nickel  Silver  — 

Lead  Bismuth 

Tin  Antimony 

7.  Nitric  Acid,  sp.  gr.  1-48  (Faraday). 
Cadmium  +  Iron  Silver 

Zinc  Bismuth  Nickel— 

Lead  Copper 

Tin  Antimony 

8.  Concentrated  Nitric  Acid  (De  la  Rive). 
Tin  +  Copper  Silver 

Zinc  Lead  Peroxide  of  Iron- 

Iron  Mercury 

9.  Pure  Dilute  Hydrofluoric  Acid  of  IV  per  cent.  (Gore). 

Aluminium  +  Lead  Bismuth 

Zinc  Silicon  Copper 

Magnesium  Iron  Silver 

Thallium  Nickel  Gold 

Cadmium  Cobalt  Gas-carbon 

Tin  Antimony  Platinum  — 

10.  Pure  Dilute  Hydrofluoric  Acid  of  '28  per  cent.  (Gore). 

Zinc  +  Nickel  Gas-carbon 

Magnesium  Cobalt  Platinum 

Aluminium  Antimony  Rhodium 

Thallium  Bismuth  Palladium 

Indium  Mercury  Tellurium 

Cadmium  Silver  Osmi-iridium 

Tin  Copper  Gold 

Lead  Arsenic  Iridium  — 

Silicon  Osmium 

Iron  Ruthenium 


Chemico-Electric  Series.  65 

II.  Aqueous  Potash  or  Soda  (H.  Davy). 

Alkali-metals  +  Copper  Gold 

Zinc  Iron  Platinum  — 

Tin  Silver 

Lead  Palladium 

12.  Solution  cf  Potash  or  Soda,  strong  or  weak  (Faraday). 

Zinc  +  Lead  Nickel 

Tin  Bismuth  Silver  — 

Cadmium  Iron 

Antimony  Copper 

13.  Solution  of  Potash  or  Soda,  sp.  gr.  1-33  (Pfaff). 

Tin  +  Copper  Steel 

Zinc  Gold  Silver  - 

Antimony  Platinum 

Lead  Bismuth 

14.  Aqueotis  Ammonia,  sp.  gr.  '95  (Pfaff). 

Zinc  +  Lead  Copper  — 

Tin  Silver 

15.  i  part  of  Cyanide  of  Potassium  in  8  parts  of  Water  (Poggendorff). 

Amalgamated  Zinc  +  Nickel  Iron 

Zinc                                Antimony  Platinum 

Copper                          Lead  Cast-iron 

Cadmium                      Mercury  Coke  — 
Tin                                 Palladium 
Silver                            Bismuth 

1 6.  Dilute  Yellow  Sulphide  of  Potassium  (Faraday). 
Zinc  +  Silver  Bismuth 
Copper                         Lead  Iron  — 
Cadmium                     Antimony 

Tin  Nickel 

17.  Dilute  Hydrosulphate  of  Potassium  (H.  Davy). 
Zinc  +  Bismuth  Gold 

Tin  Silver  Charcoal  — 

Copper  Platinum 

Iron  Palladium 

F 


66  The  Art  of  Electro- Metallurgy. 


18.   Coloiirless  Solution  of  Sulphide  of  Potassium  (Faraday). 

Cadmium  +  Antimony  Nickel 

Zinc  Silver  Iron  — 

Copper  Lead 

Tin  Bismuth 


19.  Solution  of  Sal-ammoniac  (Poggendorff ). 


Zinc  + 
Cadmium 

Magnetic  Iron 
German-silver 

Copper  pyrites 
Tellurium 

Manganese 
Lead 

Cobalt 
Bismuth 

Gold 
Galena 

Tin 
Iron 

Antimony 
Arsenic 

Coke 
Platinum 

Steel 
Uranium 

Chromium 
Silver 

Plumbago 
Peroxide  of  Man^ 

Brass 

Mercury 

ganese  — 

20.  Solution  of  Common  Salt  (Fechner). 

Zinc  +  Antimony  Gold 

Lead  Bismuth  Platinum 

Tin  Copper 

Iron  Silver 

21.  Fused  Boracic  Acid  (Gore). 

Iron  +  Platinum  Silver  — 

Silicon  Gold 

Carbon  Copper 

22.  Fused  Phosphoric  Acid  (Gore). 

Zinc  +  Copper  Platinum 

Iron  Silver 


23.  Fused  Potassic  Hydrate  (Gore).    • 

Silicon  +  Iron  Platinum 

Aluminium  Lead  Silver  — 

Zinc  Carbon 


Chemico-Electric  Relations.  67 

24.  Fused  Potassic  Carbonate  (Gore). 

Silicon  +  Carbon  Platinum  — 

Iron  Copper 

Zinc  Silver 

25.  Fused  Potassic  Chloride  (Gore). 

Aluminium  +  Iron  Silver 

Zinc  Copper  Platinum  — 

26.  Fused  Potassic  Fluoride  (Gore). 

Palladium  +  Platinum  Iridium  — 

Gold 

27.  Fused  Ammonic  Nitrate  (Gore-). 

Magnesium  +  Silver  Silicon 

Zinc  Tin  Carbon 

Lead  Aluminium  Platinum  — 

Copper  Iron 

Additional  information  respecting  the  chemico-electric 
relations  of  metals  in  aqueous  solutions  will  be  found  scat- 
tered throughout  the  book  under  the  headings  of  the  respec- 
tive metals,  and  for  additional  tables  of  the  electrical  relations 
of  metals  in  fused  substances  see  '  Philosophical  Magazine,' 
June  1864 ;  'Chemical  News,'  vol.  ix.,  p.  266. 

The  earliest  kinds  of  voltaic  batteries  were  composed  of 
two  metals  immersed  in  one  liquid,  and  from  the  outset  zinc 
appears  to  have  been  almost  the  only  metal  employed  as  the 
positive  element.  The  currents  obtained  from  them  were 
stronger  in  proportion  as  the  two  metals  were  further  asunder 
in  the  general  series  (p.  61) ;  thus  they  were  stronger 
when  silver  was  substituted  for  copper,  and  platinum  or 
carbon  for  silver,  as  the  negative  element ;  and  they  were 
obtained  still  stronger  by  selecting  from  the  special  series 
the  most  suitable  liquid  in  which  to  immerse  them.  It  was 
practically  by  selecting  metals  and  liquids  in  accordance 

F  2 


68  The  A  rt  of  Electro- Metallurgy. 

with  these  series,  and  especially  those  which  were  the  most 
durable  and  least  expensive,  that  the  earlier  kinds  of  bat- 
teries were  invented.  No  powerful  battery  is  composed  of 
two  metals  which  lie  close  together  in  the  series,  such  for 
instance  as  zinc  with  cadmium,  tin,  lead,  or  iron  in  dilute 
sulphuric  acid.  The  chief  batteries  of  this  class,  i.e.  of  two 
metals  immersed  in  one  liquid,  are  the  old  zinc  and  copper 
one,  Cruickshank's,  Wollaston's,  and  Smee's. 

The  value  of  cyanide  solutions,  for  the  purposes  of 
electro-plating,  is  also  largely  dependent  upon  the  electrical 
relations  of  the  baser  metals  to  gold  and  silver  in  such 
liquids.  If  we  refer  to  Tables  i  to  12  (pp.  63,  64)  we  may 
perceive  that  in  aqueous  acids  the  baser  metals  are  high  up 
in  the  lists,  and  more  electro-positive,  and  gold,  silver,  and 
copper  either  lower  or  a  long  way  down  ;  but  in  aqueous 
cyanide  of  potassium  (Table  15),  or  sulphide  of  potassium 
(Tables  16,  17,  18),  each  of  them  strongly  alkaline  liquids, 
copper  and  silver  are  much  higher  up,  and  iron  much  lower 
down ;  and  in  consequence  of  this  the  anode  of  nobler 
metal  is  more  easily  dissolved,  and  a  receiving  surface  of  iron 
is  less  corroded. 

The  electrical  relations  of  metals  and  carbon,  &c.,  in 
fused  substances  have  not  yet  found  to  any  notable  extent 
similar  practical  applications,  but  it  is  not  improbable  that 
some  will  be  found,  because  they  hold  out  a  prospect  of  ob- 
taining electric  currents  by  means  of  the  combustion  of  coke. 
'  The  discovery  of  some  suitable  fused  salt  or  mixture,  in  which 
carbon  is  highly  electro-positive  at  a  high  temperature  to  iron, 
nickel,  or  other  infusible  and  also  in  other  respects  suitable 
conductor,  would  probably  prove  a  cheap  and  powerful  source 
of  electricity  ;  cheap,  because  of  the  low  chemico-electric 
equivalent  of  carbon  in  relation  to  that  of  zinc,  and  the  low 
price  of  coke  and  gas-graphite ;  and  powerful,  because  of  the 
intense  affinity  of  carbon  for  oxygen  at  high  temperatures, 
sufficient  indeed  to  set  the  alkali  metals  free  from  their 
oxides.  The  nearest  approach  to  this  object  in  these  experi- 


CJiemico- Electric  Relations.  69 

ments*  (in  experiments  with  metals  in  fused  substances) 
'  was  obtained  with  carbon  and  nickel,  immersed  in  a  fused 
mixture  of  soda,  lime,  and  silica,  i.e.  in  a  species  of  glass ' 
('  Philosophical  Magazine,'  June  1864  ;  '  Chemical  News,', 
vol.  ix.,  1864,  p.  266). 

2.  By  immersion  of  one  metal  in  two  liquids. — If  two 
pieces  of  the  same  metal  are  immersed  in  two  different  con- 
ducting liquids,  the  liquids  being  in  contact  with  each  other 
through  the  medium  of  a  porous  partition   or  other  suitable 
means,  such  as  placing  the  two  liquids  in  the  two  legs  of  a 
bent  glass  tube,  &c.,  an  electric  current  is  produced.    A  large 
number  of  instances  of  currents  generated  by  means  of  this 
arrangement  are  described  in  Gmelin's  '  Handbook  of  Che- 
mistry,' vol.  i.,  p.  397,  and  one  or  two  voltaic  batteries  have 
been  constructed,  according  to  it,  but  have  not  come  into 
extensive  use. 

3.  By  immersion  of  two  metals  in  two  liquids. — Any  two 
metals  immersed  in  any  two  conducting  liquids  which  are  in 
mutual  contact  will  also  produce  an  electric  current,  and 
the  strongest  voltaic  currents  are  obtained  by  means  of  this 
arrangement,  because  there  is  not  only  an  electrical  and 
chemical  difference  of  metal,  but  also  of  liquid.     Daniell's; 
Bunsen's,  Grove's,  and  many  other  batteries,  are  of  this  kind. 

The  particular  liquid  in  which  the  most  positive  metal 
is  the  most  positive  is  not  necessarily  the  same  liquid  as  that 
in  which  the  most  negative  metal  is  the  most  negative,  and 
therefore  a  one-liquid  battery  does  not  give  the  strongest 
current ;  but  this  arrangement  of  two  metals  and  two  liquids 
enables  us  to  combine  the  advantages  of  both  liquids,  and 
thus  obtain  a  more  powerful  current. 

A  very  large  number  of  batteries  have  been  devised  and 
constructed  in  accordance  with  one  or  other  of  these  arrange- 
ments, and  many  are  in  practical  use.  The  particular  kinds 
of  them  which  have  been  employed  for  the  purposes  of 
electro-metallurgy  will  be  described  in  the  practical  division 
of  this  book. 


70  The  A  rt  of  Electro-Metallurgy. 

Voltaic  currents. — As  the  origin  of  the  currents  in  voltaic 
batteries,  the  terms  tension,  potential,  intensity  of  current, 
quantity  of  current,  electro-motive  force,  &c.,  are  fully  ex- 
plained in  another  book  of  this  series,  viz.  the  '  Treatise  on 
Electricity  and  Magnetism/  by  Fleeming  Jenkin,  F.R.S.,  I 
shall  say  no  more  than  is  requisite  on  those  points,  but  refer 
the  reader  to  that  treatise  for  fuller  information. 

The  electrical  relations  of  metals  in  liquids  are  the  chief 
source  of  all  voltaic  current-,  and  the  main  fact  upon  which 
the  action  of  all  voltaic  batteries  depends.  If  two  different 
metals  are  immersed  in  a  conducting  liquid,  or  in  two  such 
liquids,  the  liquids  being  in  mutual  contact,  and  the  metals 
united  by  a  wire,  a  constant  state  of  electric  difference  is 
produced  in  them  by  their  mutual  contact,  and  by  a  differ- 
ence of  chemical  action  of  the  liquid  or  liquids  upon  them ; 
and  this  is  the  commencement  of  all  voltaic  action,  and  the 
origin  of  electro-motive  force.  The  particular  kind  of  chemical 
action  which  is  the  main  source  of  the  current  in  nearly  all 
such  batteries  is  the  union  of  the  zinc  with  the  oxygen  of 
the  liquid  in  contact  with  it. 

Electro-motive  force. — The  electro-motive  force,  or  strength 
of  the  current  to  overcome  resistance,  depends  upon  the 
degree  of  difference  of  strength  of  chemical  affinity  of  the 
two  metals  for  the  electro-negative  constituents  of  the  liquid. 
The  farther  asunder,  therefore,  the  two  metals  are  in  the 
chemico-electric  series  (p.  61),  the  greater  usually  is  the 
difference  of  intensity  of  chemical  action  of  ordinary  acid 
liquids  upon  them,  and  the  stronger  also  is  the  electro-motive 
force.  This  general  truth  may  be  easily  verified  by  con- 
necting pieces  of  platinum  and  copper  with  a  galvanometer, 
and  immersing  their  ends  in  dilute  nitric  acid  whilst  watching 
the  needle  ;  then  make  a  similar  experiment  with  copper  and 
zinc  in  dilute  sulphuric  acid  ;  also  with  zinc  and  magnesium 
in  extremely  dilute  sulphuric  acid  ;  and  it  will  be  found  that 
in  each  case  the  current  proceeds  from  the  metal  which  is 
most  acted  upon,  through  the  liquid  to  the  other  metal.  The 


Electro- Motive  Force.  71 

electro-motive  force  evidently  depends  also  upon  a  more 
fundamental  point,  which  as  yet  has  been  but  comparatively 
little  studied,  viz.  upon  the  kind  of  chemical  affinity  exer- 
cised between  the  positive  metal  and  the  negative  consti- 
tuents of  the  liquid  ;  for  instance,  copper  is  powerfully 
corroded  by  nitric  acid,  but  although  the  intensity  of  chemi- 
cal attraction  is  great  in  this  case,  the  electro-motive  force 
generated  is  comparatively  feeble.  I  have  made  some 
experiments  upon  this  point.  The  ordinary  unit  of  electro- 
motive force  employed  in  this  country  is  termed  a  '  volt ' 
(see  Jenkin's  'Treatise  on  Electricity  and  Magnetism,' 
p.  159  ;  also  Appendix,  p.  387  of  this  work). 

Potential  and  tension. — Previous  to  the  completion  of 
the  circuit  and  formation  of  an  unimpeded  current,  the  free 
ends  of  the  polar  wires  attached  to  the  two  metals  are 
charged  with  the  two  kinds  of  electricity  in  an  accumulated 
or  free  static  condition,  and  are  in  a  state  si  electric  potential, 
i.e.  possessing  a  capability  of  doing  electric  work.  These 
accumulated  electricities  in  the  wires  may  be  detected  by 
means  of  a  very  delicate  electroscope.  The  free  electricities 
are  also  in  a  state  of  tension,  constantly  tending  to  escape 
and  unite ;  and  their  degrees  of  tension  may  be  measured 
by  means  of  an  electrometer ;  the  degree  of  tension,  how- 
ever, in  a  single  voltaic  cell  is  extremely  small,  and  has  been 
estimated  to  be  about  ten  million  times  less  than  that  of  an 
ordinary  frictional  electric  machine. 

Current;  strength  of  current. — The  continual  union  ot 
the  two  electricities  through  the  connecting  wire,  or  other 
conductor,  constitutes  an  electric  current.  Any  given  voltaic 
battery  can  only  yield  a  given  maximum  strength  of  current. 
The  strength  is  the  amount  or  quantity  of  electric  force  which 
flows  through  any  given  section  of  the  circuit  in  a  given  period 
of  time.  It  depends  upon  two  conditions,  viz.  the  electro- 
motive force  of  the  battery,  and  the  total  amount  of  resist- 
ance in  the  circuit.  The  strength  of  the  current  is  equal 
to  the  electro-motive  force  divided  by  the  resistance ;  this 


72  The  Art  of  Electro- Metallurgy. 

is  known  as  Ohm's  law ;  it  is  directly  proportional  to  the 
electro-motive  force,  and  inversely  proportional  to  the  resist- 
ance ;  if  the  resistance  remains  the  same,  and  the  electro- 
motive force  varies,  the  strength  is  directly  proportional 
to  the  electro-motive  force ;  and  if  the  electro-motive 
force  remains  the  same,  and  the  resistance  varies,  it  is  in- 
versely proportional  to  the  whole  of  the  resistance  in  the 
circuit  (see  Appendix,  p.  387). 

Resistance;  'intensity*  of  current. — The  total  resistance 
in  the  circuit  is  usually  divided  into  internal,  or  that  in  the 
battery  itself ;  and  external,  or  that  in  the  connecting  wires 
and  other  portions  of  the  circuit  outside  the  battery.  If  the 
external  resistance  is  much  less  than  that  of  one  cell,  as 
when  the  poles  of  a  single  voltaic  cell  are  connected  by  a 
short  and  thick  copper  wire,  any  addition  to  the  number  of 
cells  in  the  battery  will  produce  no  perceptible  increase  of 
current,  because  by  that  addition  we  augment  the  internal 
resistance  as  fast  as  we  increase  the  electro-motive  power. 
But  if  the  external  resistance  is  much  greater  than  the  resist- 
ance in  the  battery,  any  addition  to  the  number  of  cells 
will  produce  a  nearly  proportionate  increase  in  the  quantity 
or  strength  of  the  current,  because  we  then  increase  the 
electro-motive  force  much  faster  than  we  augment  the  total 
amount  of  resistance. 

A  current  which  is  but  little  diminished  in  amount  by  the 
introduction  of  a  given  external  resistance  is,  in  common 
language,  said  to  possess  great  '  intensity ' ;  but  the  differ- 
ence of  effect  produced  by  means  of  a  current  from  one  cell 
and  that  from  many,  does  not  arise  from  any  real  difference 
in  the  nature  of  the  currents  in  the  two  cases,  but  from  the 
difference  of  proportion  of  external  to  internal  resistance. 
No  difference  has  hitherto  been  recognised  in  any  two  cur- 
rents of  equal  quantity  per  minute,  obtained  from  different 
voltaic  sources. 

Measurement  of  current. — The  quantity  of  electricity 
circulating  may  be  measured  by  the  amount  of  electric  work 


Measurement  of  Current. 


73 


FIG.  16. 


performed,  and  the  strength  of  the  current  by  the  amount  of 
such  work  done  in  a  given  period  of  time. 

The  instruments  usually  employed  for  this  purpose  are 
either  a  galvanometer  or  a  voltameter.  The 'construction, 
action,  and  mode  of  using  a  galvanometer  are  already  fully 
described  in  the  '  Treatise  on  Electricity  and  Magnetism '  of 
this  series,  p.  187.  One  suitable  for 
use  in  electrolytic  experiments  should 
offer  but  little  resistance  to  the  passage 
of  the  current,  and  what  is  termed  '  a 
tangent '  one  may  be  conveniently  em- 
ployed, because  the  magnetic  action  of 
the  current  upon  the  needle  is  then 
much  less  powerful. 

Voltameters  are  of  different  kinds ; 
that  originally  employed  by  Faraday 
contained  a  mixture  of  sulphuric  acid 
and  water  as  the  electrolyte.  A  water 
voltameter  is  shown  in  the  annexed 
sketch,  Fig.  16.  Two  graduated  glass 
tubes,  A  and  B,  open  at  the  bottom,  and  provided  with 
stop-cocks  at  their  upper  ends,  are  inverted  over  two  large 
plates  of  platinum,  C  and  D,  which  are  connected  to  the 
binding  screws,  by  means  of  wires  beneath.  The  outer  glass 
jar  is  nearly  filled  with  a  previously- cooled  mixture  of  about 
3!  or  4  measures  of  distilled  water  and  i  measure  of  pure  sul- 
phuric acid,  the  acid  being  added  to  the  water,  not  the  reverse. 
On  passing  the  current  to  be  measured  from  C  to  D,  oxygen 
collects  in  C  and  hydrogen  in  D,  and  the  quantity  of  elec- 
tricity passed  varies  directly  as  the  amount  of  gas  evolved. 

In  this  form  of  voltameter  a  little  error  arises  in  conse- 
quence of  a  small  portion  of  the  gas  being  dissolved  in  the 
xvater,  and  also  from  unequal  pressure  of  the  liquid  upon 
different  quantities  of  gas  ;  if  also  the  current  to  be  measured 
is  one  of  low  electro-motive  force,  its  amount  is  largely 
diminished  by  the  resistance  in  the  voltameter  itself. 


74  The  A  rt  of  Electro-Metallurgy. 

An  arrangement  which  offers  less  conduction  resistance, 
and  which  is  very  convenient,  consists  in  passing  the  current 
through  two  large  electrodes  (the  cathode  being  a  thin  one) 
of  pure  and  clean  sheet  copper,  immersed  in  a  nearly  satu- 
rated solution  of  sulphate  of  copper,  to  which  has  been  sub- 
sequently added  about  one-sixth  its  bulk  of  pure  dilute  sul- 
phuric acid,  and  carefully  weighing  the  cathode  before  and 
after  the  experiment  Each  atomic  weight,  63-5  parts  in 
grains,  may,  as  copper  is  a  dyad  (see  p.  41),  be  said  to 
represent  two  equivalents  of  electricity. 

Amounts  of  electricity  produced  by  different  metals. — As 
the  proportionate  number  of  atomic  weights  of  a  substance 
dissolved  or  deposited  by  electrolysis  depends  upon  the 
*  valency'  of  the  elements  (see  p.  41),  so  in  like  manner 
does  the  quantity  of  the  current  generated  in  a  voltaic 
battery  depend  upon  the  same  condition.  Thus  one  atomic 
weight  (say  in  grains)  of  a  monad  element  will  produce  one 
equivalent  of  electricity,  a  dyad  two,  a  triad  three,  a  tetrad 
four,  &c.  Whilst  it  is  the  degree  of  intensity  of  chemical 
attraction  of  the  positive  metal  by  the  negative  element  of 
the  liquid  in  the  battery  which  determines  the  electro-motive 
force  of  the  current,  it  is  the  quantity  of  the  substances 
attracted  which  determines  its  amount. 

Relation  of  the  quantity  of  chemical  action  in  the  battery,  to 
that  in  the  depositing  vessel. — The  relations  of  the  electric 
current,  both  to  the  quality  and  quantity  of  electrolytic  effect, 
have  already  been  described  (p.  35  to  45);  and  those  re- 
lations are  the  same  whether  the  current  producing  the  elec- 
trolysis is  generated  in  the  electrolytic  vessels  themselves, 
or  in  separate  batteries,  or  other  electro-motors.  And,  as 
a  chemico-electric  equivalent  of  metal  dissolved  in  the 
battery  generates  an  equivalent  of  electricity,  and  an 
equivalent  of  electricity  deposits  an  equivalent  of  metal  in 
the  deposit-cell  (pp.  42,  44),  we  may  now  say  that,  usually, 
for  each  chemical  equivalent  of  substances  dissolved,  set  free,  or 
formed,  in  each  cell  of  the  battery,  a  chemical  equivalent  of  other 


Definite  Electro-  Chemical  A  ction.  7 5 

substance  is  dissolved,  set  free  or  formed,  in  each  depositing  vessel, 
in  the  same  circuit ;  and  that  this  equivalency  of  action 
throughout  the  circuit  is  due  to  the  fact  that  each  chemical 
equivalent  of  any  substance  has  associated  with  it  an  equal 
amount  of  electricity.  This  is  the  law  of  definite  electro- 
chemical action. 

Faraday  established  that  law.  He  found  that  *  if  the 
current  of  a  battery  be  passed  through  a  voltameter  contain- 
ing dilute  sulphuric  acid  and  platinum  electrodes,  and  thence 
by  means  of  a  platinum  wire  entering  the  upper  end,  and  con- 
veying positive  electricity  into  a  glass  tube  containing  fused 
protochloride  of  tin,  and  having  inserted  into  its  lower  end 
a  platinum  wire,  which  serves  as  the  negative  electrode, 
then  for  every  9  parts  of  water  decomposed  in  the  volta- 
meter 58*53  parts  of  tin  are  deposited  on  the  last-mentioned 
wire  '  (the  atomic  weight  of  tin  is  1 18).  '  When  fused  chloride, 
iodide,  oxide,  and  borate  of  lead  were  treated  in  a  similar 
manner,  the  quantity  of  lead  obtained  was  too  small  in  pro- 
portion to  the  water  decomposed,  viz.  to  9  parts  of  water, 
ioo'8,  89*,  93*2,  and  101*3  lead,  whereas  the  atomic  weight 
of  lead  is  207'  (or  103*5  x  2>  lea-d  being  a  dyad).  'The  cause 
of  the  deficiency  is,  probably,  that  a  portion  of  the  precipi- 
tated lead  was  redissolved  by  the  anion  ;  a  kind  of  circum- 
stance which  occasionally  happens.  When  two  silver  wires 
are  introduced  as  electrodes  into  fused  chloride  of  silver,  the 
weight  of  the  positive  electrode  diminishes  almost  exactly 
1 08 'i  parts  for  every  9  parts  of  water  decomposed  in  the 
voltameter,  whilst  that  of  the  negative  electrode  increases  by 
the  same  quantity.  Chloride  and  iodide  of  lead  treated 
in  the  same  manner,  lead  being  used  as  the  positive  electrode, 
gave  iof'5,  and  103*5  ^ea(i  f°r  every  9  parts  of  water.' 

According  to  Quincke,  the  force  tending  to  separate  the 
constituents  of  an  electrolyte  is  proportional  to  the  density 
of  the  current,  i.e.  to  the  strength  of  the  current  per  unit  of 
sectional  area  of  the  liquid  ;  it  also  increases  with  the  electro- 
motive force  of  the  current  employed,  and  is  inversely  pro- 


76  The  Art  of  Electro-Metallurgy. 

portional  to  the  length,  but  independent  of  the  cross-section 
and  of  the  conductivity  of  the  liquid,  if  the  resistance  of  the 
remainder  of  the  circuit  is  small  in  comparison  with  that 
of  the  electrolyte  ('Journal  of  the  Chemical  Society/  vol.  x., 
p.  208). 


PRACTICAL  DIVISION. 
SECTION  A. 

General  methods  of  depositing  metals. — There  are  various 
methods  which  either  have  been  or  are  still  employed  in 
depositing  metals  from  their  solutions  for  practical  purposes, 
and  they  may  be  classed  as  follows — ist.  By  immersing  one 
metal  in  one  liquid,  as,  for  instance,  by  immersing  steel  or  iron 
in  a  slightly-acidulated  solution  of  sulphate  of  copper.  2nd. 
By  immersing  two  metals  in  one  liquid,  as  by  immersing  the 
article  to  be  coated  in  contact  with  zinc  or  other  sufficiently 
positive  metal  in  the  particular  metallic  solution.  3rd.  By 
immersing  one  metal  in  two  liquids,  as,  for  instance,  if  a  deep 
glass  vessel  be  half  filled  with  a  saturated  aqueous  solution 
of  cupric  sulphate,  the  vessel  be  then  nearly  filled  with  water 
containing  a  small  quantity  of  sulphuric  acid,  poured  in 
quietly  so  as  not  to  mix  with  the  copper  solution,  and  a 
bright  rod  of  copper,  as  deep  as  the  vessel,  be  allowed  to 
remain  in  a  vertical  position  in  the  liquid  during  twenty-four 
hours  without  disturbance ;  the  upper  half  of  the  rod  will 
slowly  corrode  and  dissolve,  whilst  the  lower  half  will  receive 
a  deposit  of  copper.  4th.  By  immersing  two  metals  in  two 
liquids,  as  in  the  ordinary  '  single  cell '  electrotype  appa- 
ratus. 5th.  By  the  separate  current  plan,  as  when  a  voltaic 
battery,  magneto-machine,  or  thermo-electric  pile  is  em- 
ployed with  a  separate  depositing  vessel. 

Under  each  of  these  classes  will  be  mentioned  a  number 
of  experiments  made  by  the  author,  and  it  is  desirable  that 


Methods  of  Electro-Deposition.  TJ 

the  student  should  repeat  a  few  of  them,  in  order  to  fix  the 
general  principles  more  firmly  in  his  memory. 

Method  No.  i. — Deposition  by  immersing  one  metal  in  one 
liquid  (see  Fig.  17).  With  aqueous  solutions  of  the  following 
salts  I  obtained  the  effects  mentioned.  In  FIG.  17. 

hydrochlorate  of  terchloride  of  antimony  (a 
solution  of  terchloride  of  antimony  in  hy- 
drochloric acid),  as  prepared  for  pharma- 
ceutical purposes,  zinc,  bismuth,  tin,  lead, 
brass,  and  german- silver  became  coated 
with  antimony  ;  whilst  antimony,  nickel, 
silver,  gold,  and  platinum  did  not. 

Chloride  of  bismuth. — Zinc,  tin,  lead 
and  iron  deposited  the  bismuth  upon 
themselves,  whilst  antimony,  bismuth, 
copper,  brass,  german -silver,  gold,  and  platinum  did  not. 

Tetrachloride  of  platinum. — Platinum  was  deposited  from 
a  solution  of  its  chloride  by  arsenic,  antimony,  tellurium, 
bismuth,  zinc,  cadmium,  tin,  lead,  iron,  cobalt,  nickel, 
copper,  brass,  german-silver,  mercury,  and  silver ;  but  not 
by  gold  or  platinum. 

Gold  solutions. — From  an  acid  solution  of  terchloride 
of  gold,  the  base  metals,  likewise  mercury,  silver,  plati- 
num, and  palladium,  deposited  gold  in  the  metallic 
state ;  arsenic  rapidly  deposited  gold  in  this  solution ; 
antimony,  tellurium,  and  bismuth  became  gilded  ;  zinc, 
cadmium,  lead,  iron,  cobalt,  mercury,  silver,  platinum,  and 
palladium  deposited  the  gold.  In  a  solution  of  the  double 
cyanide  of  gold  and  potassium,  zinc  quickly  became  gilded, 
and  copper,  brass,  and  german-silver  slowly,  whilst  antimony, 
bismuth,  tin,  lead,  iron,  nickel,  silver,  gold,  and  platinum 
did  not. 

Silver  solutions. — The  following  metals,  viz.  manganese, 
arsenic,  antimony,  bismuth,  zinc,  cadmium,  tin,  lead,  iron, 
copper,  and  mercury  deposited  silver  from  its  solutions  in 
the  metallic  state.  An  aqueous  solution  of  nitrate  of  silver 


?8  The  A  rt  of  Electro-Metallurgy. 

yielded  its  metal  to  manganese,  arsenic,  antimony,  bismuth, 
zinc,  tin,  lead,  iron,  nickel,  copper,  brass,  and  german-silver  ; 
but  not  to  silver,  sold,  or  platinum ;  lead  and  tin  deposited 
the  silver  most  quickly ;  then  followed  the  other  metals  in 
this  order :  cadmium,  zinc,  copper,  bismuth,  antimony, 
arsenic,  mercury.  Arsenic  deposited  silver  from  the  alcoholic 
solution  of  nitrate  of  silver  ;  antimony  received  a  coating  of 
silver  either  in  the  aqueous  sulphate  or  alcoholic  nitrate  ; 
bismuth  deposed  silver  from  the  alcoholic  nitrate,  but  not 
from  the  aqueous  sulphate ;  zinc  received  a  silver  deposit  in 
the  alcoholic  nitrate ;  tin  became  silvered  in  the  alcoholic 
nitrate,  but  more  quickly  in  the  aqueous  sulphate ;  iron 
deposited  silver  from  the  sulphate  of  silver,  but  not  from  the 
alcoholic  nitrate  ;  copper  deposited  it  from  the  aqueous  sul- 
phate or  alcoholic  nitrate ;  brass  and  the  alloys  of  silver,  with 
zinc,  tin,  or  lead,  deposited  silver  from  silver  solutions  com- 
pletely. In  a  solution  of  the  double  cyanide  of  silver  and  potas- 
sium (the  ordinary  silver-plating  liquid),  zinc,  lead,  and 
copper  became  silvered  ;  also  brass  and  german-silver,  but 
more  slowly  ;  whilst  antimony,  bismuth,  tin,  iron,  nickel, 
silver,  gold,  and  platinum  did  not. 

Mer cur ous  salts. — Solutions  of  mercurous  salts  have  their 
metal  deposited  by  arsenic,  antimony,  bismuth,  zinc,  cad- 
mium, tin,  lead,  iron,  copper,  and  brass,  also  by  the  alloys 
of  silver  with  zinc,  tin,  lead,  or  copper. 

Nitrate  of  mercury. — A  solution  of  nitrate  of  mercury 
yielded  its  metal  to  bismuth,  zinc,  cadmium,  lead,  iron,  or 
copper,  and  if  acidulated  with  nitric  acid,  to  antimony  also, 
but  not  to  silver,  gold,  or  platinum. 

Acetate  of  mercury. — Iron  deposited  mercury  from  a 
solution  of  this  salt. 

Sulphate  of  copper. — In  a  solution  of  sulphate  of  copper, 
zinc,  tin,  lead,  and  iron  became  coated  with  copper,  whilst 
antimony,  bismuth,  nickel,  copper,  silver,  gold,  and  platinum 
did  not. 

Cupric  chloride. — In  a  solution   of  chloride  of  copper, 


Methods  of  Electro-Deposition.  79 

bismuth,  zinc,  tin,  lead,  and  iron  received  a  copper  deposit ; 
whilst  antimony,  nickel,  copper,  silver,  gold,  and  platinum 
did  not. 

Nitrate  of  copper. — In  a  solution  of  nitrate  of  copper, 
zinc,  tin,  lead,  and  iron  became  coated ;  whilst  antimony, 
bismuth,  nickel,  copper,  silver,  gold,  and  platinum  did  not. 

AmmoniO'Chlorides  of  copper. — With  a  solution  of  sub- 
chloride  of  copper  in  liquid  ammonia,  or  of  black  oxide  of 
copper  in  a  solution  of  sal-ammoniac,  zinc  received  a  deposit ; 
whilst  antimony,  bismuth,  tin,  lead,  iron,  nickel,  copper, 
silver,  gold,  or  platinum  did  not. 

Ferrous  sulphate. — '  Zinc/  as  Fischer  says,  '  immersed  in 
a  perfectly  neutral  solution  of  ferrous  sulphate  (protosulphate 
of  iron),  contained  in  a  stoppered  bottle,  throws  down  me- 
tallic iron,  which  is  deposited  partly  on  the  zinc  ; '  but,  in  my 
experience,  with  this  solution  neither  antimony,  bismuth,  tin, 
lead,  iron,  nickel,  copper,  brass,  german-silver,  silver,  gold, 
or  platinum  received  any  metallic  deposit. 

Hyponitrite,  nitrate,  or  acetate  of  lead. — In  a  solution  of 
hyponitrite,  nitrate,  or  acetate  of  lead,  zinc  received  a  coating 
of  lead ;  whilst  antimony,  bismuth,  tin,  lead,  iron,  nickel, 
copper,  brass,  german-silver,  silver,  gold,  and  platinum  re- 
ceived no  deposit. 

Stannous  chloride. — In  a  solution  of  stannous  chloride, 
zinc  and  lead  become  tinned  ;  whilst  antimony,  bismuth,  tin, 
iron,  nickel,  copper,  brass,  german-silver,  silver,  gold,  and 
platinum  receive  no  deposit. 

Sulphate,  chloride,  nitrate,  or  acetate  of  zinc. — In  a  solution 
of  either  sulphate,  chloride,  nitrate,  or  acetate  of  zinc,  neither 
antimony,  bismuth,  zinc,  tin,  lead,  iron,  nickel,  copper,  brass, 
german-silver,  silver,  gold,  or  platinum  became  coated  with 
zinc. 

Observations  upon  class  of  instances  No.  i. — In  reviewing 
all  these  instances,  we  may  make  the  following  observations : 
ist,  that  various  metals  by  mere  immersion  in  solutions  of 
other  metals,  at  the  ordinary  temperature  of  the  atmosphere, 


80  The  A  rt  of  Electro-Metallurgy. 

sometimes  become  coated  with  a  deposit  of  metal,  and  some- 
times not ;  2nd,  that  a  metal  rarely  becomes  coated  by  mere 
immersion  in  a  solution  of  the  same  metal ;  for  instance, 
zinc  does  not  become  coated  with  zinc  in  a  solution  of  sul- 
phate of  zinc  (see  p.  79),  copper  with  copper  in  a  solution  of 
its  sulphate,  gold  with  gold  in  its  chloride,  £c. ;  3rd,  that  the 
baser  metals,  especially  zinc,  cadmium,  tin,  lead,  and  iron, 
become  coated  more  frequently  than  the  noble  metals, 
especially  gold  and  platinum  •  4th,  that  solutions  of  base 
metals,  especially  of  zinc  and  iron,  yield  their  metal  less 
frequently  than  those  of  the  noble  metals,  especially  those  of 
gold  and  platinum  ;  5th,  that  of  all  the  ordinary  metals  men< 
tioned  in  the  foregoing  instances,  zinc  deposits  metal  from  the 
greatest  number  of  solutions,  and  appears  to  have  the  strong- 
est depositing  power ;  6th,  that  the  coherent  and  adhesive 
deposits  obtained  are  in  all  cases  exceedingly  thin  ;  and  jth, 
that  oftentimes  the  deposited  metal,  whatever  its  kind  may 
be,  has  the  appearance  of  a  black  or  dark-coloured  powder  on 
its  surface,  especially  when  it  has  been  deposited  very  rapidly ; 
and  that  sometimes  it  exhibits  its  ordinary  colour  and 
appearance,  especially  if  its  outer  portion  is  rubbed  off. 

By  the  simple  immersion  process  a  thin  coating  only  of 
metal  is  usually  obtained,  and  even  that  is  imperfect,  because 
the  surface  to  be  coated  and  the  coating  of  metal  act  elec- 
trically as  two  different  substances,  the  former  being  electro- 
positive and  the  latter  electro-negative.  In  consequence  of 
this  electrical  difference  there  is  set  up  a  voltaic  action  at 
minute  points  all  over  the  surface  ;  this  action  is  not  per- 
ceptible at  first  because  it  is  of  microscopic  minuteness,  but 
it  gradually  spreads  from  those  points  all  over  the  surface, 
and  causes  the  metal  beneath  the  coating  to  dissolve,  and 
the  deposit  to  become  loose  and  full  of  spots. 

It  is,  however,  possible  to  coat  a  metal  perfectly  with 
another  metal  by  means  of  simple  immersion  by  adopting 
the  following  rule,  now  I  think  for  the  first  time  published. 
Take  an  electro-positive  metal,  A  (say  copper),  dip  it  into  a 


Methods  of  Electro-Deposition. 


Si 


FIG.  18. 


solution  of  a  less  positive  metal,  B  (say  mercury),  its  surface 
then  dissolves  and  a  film  of  B  is  deposited  upon  it  Now 
dip  it  into  a  solution  of  a  third  and  still  less  positive  metal, 
C  (say  gold) ;  the  film  of  B  and  also  any  non-coated  particles 
of  A  then  dissolve,  and  a  film  of  C  is  deposited  in  their 
stead.  Now  re-dip  the  metal  A  into  the  solution  of  B,  and 
any  still  non-coated  particles  of  it  are  dissolved,  and  deposit 
B  in  their  place  ;  then  dip  again  into  the  solution  of  C,  and 
a  similar  effect  takes  place  as  before.  By  thus  alternately 
dipping  the  metal  A,  into  the  solutions  of  B  and  C,  the  num- 
ber of  its  non-coated  particles  becomes  less  and  less,  until 
every  one  is  coated  with  the  metal  C  (see  p.  128).  The 
rule  is  applicable  to  various  metals  to  which  it  has  not  yet 
been  applied  ;  and  its  application  offers  an  opening  for  new 
inventions. 

To  the  simple  immersion  mode  of  depositing,  belongs 
the  process  of  tinning  brass  articles  (wash  tinning),  by  boil- 
ing them  in  water  containing  a  salt  of  tin 
and  bitartrate  of  potash ;  the  process  of 
silvering  brass  nails,  buttons,  hooks  and 
eyes,  buckles,  &c,  by  rubbing  them  with 
any  of  the  well-known  silvering  composi- 
tions moistened  with  water;  also  the  water- 
gilding  process  (see  pp.  265,  152,  127). 

Method  No.  2.  Deposition  by  two 
metals  and  one  liquid  or  *  by  simple  contact 
process '  (see  Fig.  18).  The  following  in- 
stances belong  to  the  class  of  deposition 
by  two  metals  and  one  liquid,  the  two 
metals  being  either  in  mutual  contact 
(touching  each  other  either  above  or 
beneath  the  surface  of  the  liquid),  or  connected  together  by 
a  wire. 

In  chloride  of  antimony. — On  immersing  a  piece  of  anti- 
mony in  contact  with  a  piece  of  zinc  in  a  solution  of  the 
ordinary  chloride  of  antimony,  it  received  a  coating  of  anti- 

G 


82  The  Art  of  Electro- Metallurgy. 

mony,  and  on  immersing  a  piece  of  platinum  in  contact  with 
a  piece  of  tin  in  this  liquid,  it  received  a  deposit  of  antimony ; 
but  on  immersing  a  piece  of  antimony  in  contact  with  a 
piece  of  platinum,  or  a  piece  of  platinum  in  contact  with  a 
piece  of  silver  in  this  liquid,  it  received  no  metallic  deposit. 

Chloride  of  bismuth. — In  a  solution  of  this  salt,  brass  in 
contact  with  a  piece  of  zinc,  copper  in  contact  with  tin,  or 
german-silver  with  iron,  received  a  deposit  of  bismuth ;  but 
brass  in  contact  with  a  piece  of  gold,  gold  in  contact  with 
silver,  or  german-silver  with  platinum,  received  no  deposit. 

Tetrachloride  of  platinum. — In  a  solution  of  this  salt, 
platinum  in  contact  with  zinc  became  coated  with  platinum, 
but  in  contact  with  gold  it  received  no  such  coating. 

Nitrate  of  silver. — In  a  solution  of  argentic  nitrate,  gold 
in  contact  with  zinc  received  a  deposit  of  silver,  but  in 
contact  with  platinum  it  did  not. 

Nitrate  of  mercury. — In  a  solution  of  this  salt,  silver  in 
contact  with  either  zinc  or  iron,  or  platinum  in  contact  with 
copper,  received  a  metallic  deposit ;  but  platinum  in  contact 
with  silver  did  not. 

Sulphate  of  copper. — In  a  solution  of  cupric  sulphate, 
brass  in  contact  with  zinc,  or  tin,  german-silver,  silver,  or 
platinum,  in  contact  with  iron,  received  a  deposit  of  copper ; 
whilst  silver  in  contact  with  antimony,  or  platinum  in  contact 
with  brass,  received  no  deposit 

Oxide  of  copper  in  ammonia. — In  a  solution  of  oxide  of 
copper  in  ammonia,  platinum  in  contact  with  zinc  received 
a  deposit ;  but  silver  in  contact  with  iron  did  not. 

Chloride  of  nickel  and  ammonium. — In  a  solution  of  the 
double  chloride  of  nickel  and  ammonium,  copper  in  contact 
with  zinc  received  a  deposit  of  nickel,  but  in  contact  with 
silver  it  did  not  receive  such  a  deposit. 

Protosulphate  of  iron. — With  a  saturated  solution  of  this 
salt,  platinum  in  contact  with  zinc  received  a  deposit  of  iron  ; 
but  in  contact  with  copper  it  received  no  metallic  deposit. 

Hyponitrite  of  lead. — With  a  solution  of  hyponitrite  of 


Methods  of  Electro-Deposition.  83 

lead,  either  tin,  copper,  or  brass,  in  contact  with  a  piece  of 
zinc,  received  a  deposit  of  lead  ;  but  copper  in  contact  with 
tin  or  lead,  or  brass  with  platinum,  received  no  deposit. 

Nitrate  of  lead. — With  a  solution  of  plumbic  nitrate, 
either  copper,  brass,  or  silver,  in  contact  with  zinc,  received 
a  coating  of  lead  ;  but  copper  in  contact  with  iron,  brass 
with  tin,  or  silver  with  copper,  received  no  such  coating. 

Stannous  chloride. — With  a  solution  of  this  salt,  either 
antimony,  tin,  or  copper,  immersed  in  contact  with  zinc  or 
lead,  received  a  coating  of  tin  ;  but  antimony  in  contact 
with  tin,  tin  with  silver,  copper  with  iron,  or  either  gold  or 
platinum  with  copper,  did  not  receive  a  deposit. 

Sulphate,  chloride,  or  nitrate  of  zinc. — With  a  solution  of 
either  sulphate,  chloride,  or  nitrate  of  zinc,  no  metal  of  any 
pair  of  metals,  selected  from  amongst  the  following,  received 
a  deposit  of  zinc  :  antimony,  bismuth,  zinc,  tin,  lead,  iron, 
nickel,  copper,  mercury,  silver,  gold,  platinum,  or  palladium. 

Observations  upon  class  of  instances  No.  2. — The  following 
general  observations  may  be  made  upon  the  foregoing  facts  : 
firstly,  that  in  some  instances  deposition  does,  and  in  others  it 
does  not,  occur ;  secondly,  that  a  metal  will  not  usually  cause 
another  metal  to  be  coated  by  this  method,  unless  it  can  coat 
itself  in  the  same  liquid  by  simple  immersion — for  instance, 
zinc  cannot  coat  itself  with  zinc  in  solutions  of  that  metal, 
neither  can  it  usually  cause  other  metals  to  become  coated 
with  that  metal  in  those  solutions  (see  above) ;  copper  can- 
not usually  coat  itself  with  zinc  in  a  solution  of  sulphate  of 
zinc,  or  with  tin  in  a  solution  of  chloride  of  tin,  neither  does 
it  usually  cause  silver,  gold,  or  other  metal,  to  become  coated 
with  zinc  or  tin  in  those  liquids  (see  Raoult's  experiments, 
pp.  268,  273,  276);  thirdly,  that  one  of  the  two  metals  which 
receives  a  deposit  by  this  method,  derives  its  power  of  receiv- 
ing it  by  virtue  of  its  contact  with  the  other  metal ;  fourthly, 
that  any  metal  which  has  the  power  of  coating  itself  by 
simple  immersion  in  a  given  liquid  can,  by  this  method,  cause 
other  metals  which  do  not  coat  themselves  by  simple  immer- 

G  2 


84  The  A  rt  of  Electro-Metallurgy. 

sion  in  that  liquid,  to  become  coated ;  for  instance,  zinc,  tin, 
and  iron,  coat  themselves  with  copper,  by  simple  immersion 
in  a  solution  of  sulphate  of  copper,  but  silver,  gold,  and 
platinum  do  not ;  but  if  either  of  the  former  metals  be  con- 
nected with  either  of  the  latter,  the  two  being  immersed  toge- 
ther in  that  liquid,  the  latter  metals,  as  well  as  the  former, 
will  become  coated  with  copper ;  fifthly,  that  base  metals,  and 
especially  zinc,  have  generally  the  power  of  causing  other 
metals  to  become  coated  by  this  method,  whilst  the  noble 
metals,  and  especially  gold  and  platinum,  rarely  possess  this 
power;  sixthly,  that  by  this  method,  metal  is  deposited  much 
more  frequently  from  solutions  of  the  noble  metals,  than 
from  those  of  the  base  ones ;  and,  finally,  that  thick  de- 
posits of  metal  may  be  obtained  by  this  method,  provided  the 
action  is  continued  sufficiently  long,  and  the  liquid  properly 
renewed. 

Method  No.  3. — Deposition  by  one  metal  and  two  liquids 
(see  Figs.  19,  20). — The  following  instances  belong  to  de- 
position by  the  immersion  of  one  metal  in  two  liquids, 
separated  by  a  porous  diaphragm,  the  metal  being  either  in 
two  pieces,  connected  together  by  a  wire  or  wires,  or  in  one 
piece,  and  bent  so  as  to  dip  into  both  liquids,  or  the  dia- 
phragm may  be  dispensed  with,  as  already  explained,  by 
pouring  the  lighter  liquid  carefully  above  the  other,  and 
placing  the  piece  of  metal  vertically  in  the  two  liquids 
(see  Fig.  19). 

Antimony  in  chloride  of  antimony. — Two  pieces  of  anti- 
mony, connected  together  by  a  wire  or  wires,  were  immersed, 
one  in  dilute  nitric  acid,  and  the  other  in  a  solution  of  chloride 
of  antimony ;  the  piece  in  the  dilute  acid  dissolved,  whilst 
that  in  the  chloride  solution  received  a  metallic  deposit. 

Iron  in  chloride  of  antimony. — With  iron  in  dilute  sul- 
phuric acid  on  one  side,  and  in  a  solution  of  chloride  of 
antimony  on  the  other,  the  end  in  the  metallic  solution 
received  a  deposit  of  antimony,  whilst  that  in  the  dilute  acid 
dissolved. 


MetJiods  of  Electro-Deposition. 


Antimony  in  chloride  of  bismuth. — Two   pieces  of  anti- 
mony were  immersed  in  the  previous  manner,  one  in  hydro- 

FIG.  19.  FIG.  20. 


chloric  acid,  and  the  other  in  a  solution  of  chloride  of  bis- 
muth ;  that  in  the  acid  dissolved,  and  the  other  received  a 
coating  of  bismuth. 

Bismuth  in  chloride  of  bismuth. — With  bismuth  in  hydro- 
chloric acid  on  one  side,  and  in  a  solution  of  chloride  of 
bismuth  on  the  other,  a  free  deposit  of  bismuth  was  soon 
obtained. 

Bismuth  in  nitrate  of  bismuth. — With  bismuth  in  dilute 
nitric  acid,  and  in  a  solution  of  acid  nitrate  of  bismuth,  a 
thin  deposit  of  that  metal  was  found  in  twelve  hours. 

Silver  in  sulphate  of  copper,  and  in  cyanide  of  silver 
plating  liquid. — With  silver  in  either  dilute  sulphuric  or 
dilute  nitric  acid  on  one  side,  and  in  a  solution  of  sulphate 
of  copper  on  the  other,  no  deposit  of  copper  took  place  in 
twelve  hours  •  but  with  silver  in  a  solution  of  cyanide  of  po- 


86  The  A  rt  of  Electro-Metallurgy. 

tassium  on  one  side,  and  in  the  double  cyanide  of  potassium 
and  silver  on  the  other,  a  free  deposit  of  silver  occurred  upon 
the  end  or  piece  in  the  latter  solution. 

Antimony  in  sulphate  of  copper. — With  antimony  in 
dilute  hydrochloric  acid  on  one  side,  and  in  a  solution  of 
sulphate  of  copper  on  the  other,  a  deposit  of  copper  was 
obtained. 

Platinum  in  nitrate  of  copper. — With  platinum  in  aqua 
regia  on  one  side,  and  in  either  a  solution  of  nitrate  of  cop- 
per, the  ordinary  cyanide  gilding  solution,  or  a  solution  of 
tetrachloride  of  platinum  on  the  other,  no  deposit  of  copper, 
gold,  or  platinum  occurred. 

Brass  or  copper  in  sulphate  of  copper. — With  brass  or 
copper  in  dilute  sulphuric  acid  on  one  side,  and  in  a  solution 
of  sulphate  of  copper  on  the  other,  a  deposit  of  copper  was 
obtained  in  twelve  hours ;  similarly  with  copper  in  dilute 
hydrochloric  acid,  and  in  a  solution  of  chloride  of  copper,  a 
metallic  deposit  occurred. 

Tin  in  chloride  of  tin. — With  tin  in  dilute  hydrochloric 
acid  on  one  side,  and  in  a  solution  of  stannous  chloride  on 
the  other,  a  deposit  of  tin  was  obtained. 

Copper  in  sulphate  of  zinc. — With  copper  in  dilute  sul- 
phuric, or  dilute  nitric  acid,  on  one  side,  and  in  a  solution 
of  sulphate  of  zinc  on  the  other,  no  deposit  of  zinc  oc- 
curred in  twelve  hours. 

Iron  in  sulphate  of  zinc,  and  in  sulphate  of  iron. — With 
iron  in  dilute  sulphuric  acid  on  one  side,  and  in  a  solution  of 
sulphate  of  zinc  on  the  other,  no  deposit  of  zinc  was  obtained 
in  twelve  hours ;  similarly  with  iron,  dilute  sulphuric  acid, 
and  a  solution  of  protosulphate  of  iron,  no  deposit  occurred 
in  twelve  hours. 

Zinc  in  chloride  of  zinc. — A  piece  of  zinc  was  bent  so  as 
to  dip  into  dilute  hydrochloric  acid  on  one  side,  and  into  a 
neutral  solution  of  chloride  of  zinc  on  the  other  ;  a  free  de- 
posit of  zinc  was  found  upon  the  end  in  the  metallic  solution, 
after  a  period  of  twelve  hours. 


Methods  of  Electro-Deposition.  87 

Zinc  in  sulphate  of  zinc. — With  zinc  in  dilute  sulphuric 
acid,  and  in  a  solution  of  sulphate  of  zinc,  a  free  deposit  of 
the  metal  occurred  in  twelve  hours. 

Zinc  in  acetate  of  zinc. — With  zinc  in  a  solution  of  ace- 
tate of  zinc  on  one  side,  and  in  dilute  sulphuric  acid  on  the 
other,  that  in  the  dilute  acid  dissolved,  whilst  the  other  end 
received  a  metallic  deposit. 

Observations  on  class  of  instances  No.  3. — ist,  it  appears 
that  in  this  class  also,  we  obtain  negative  as  well  as  positive 
instances  ;  2nd,  that  by  this  arrangement,  unlike  the  previous 
classes,  almost  any  metal  may  cause  the  same  metal  to  be 
deposited — for  instance,  zinc  may  deposit  zinc,  copper  de- 
posit copper,  and  silver  deposit  silver  ;  3rd,  that  by  it  even 
a  noble  metal  may  cause  the  deposition  of  a  base  metal, 
provided  we  have  a  suitable  combination  of  liquids — for 
instance,  if  a  piece  of  gold  or  silver  be  immersed  in  a  strong 
solution  of  cyanide  of  potassium  on  one  side,  and  in  a  solu- 
tion of  sulphate  of  copper  or  chloride  of  antimony  on  the 
other,  the  end  in  the  free  cyanide  solution  dissolves,  whilst 
that  in  the  copper  or  antimony  one  receives  a  deposit; 
4th,  that  the  metal  or  end  which  receives  a  deposit,  derives 
that  power  from  its  contact  with  the  metal  in  the  other  liquid; 
5th,  that,  as  a  general  rule,  base  metals  have  a  greater  power 
of  causing  deposition  by  this  method  than  the  noble  ones ; 
6th,  that  the  noble  metals  are  more  readily  and  more  often 
deposited  than  the  base  ones  ;  and,  yth,  that  we  may  produce 
thick  and  coherent  deposits. 

Method  No.  4. — Deposition  by  two  metals  and  two  liquids, 
or  'single-cell  process'  (see  Fig.  20,  also  Fig.  i,  p.  18). 
The  following  instances  belong  to  the  class  of  deposition 
produced  by  the  immersion  of  two  metals  in  two  liquids,  the 
metals  being  in  mutual  contact,  or  connected  together  by  a 
wire,  and  the  liquids  separated  by  a  porous  partition. 

Zinc  depositing  antimony. — A  piece  of  antimony  was  im- 
mersed in  a  solution  of  its  chloride,  and  a  piece  of  zinc  in 
dilute  sulphuric  acid,  and  the  two  metals  being  connected 


88  The  A  rt  of  Electro- Metallurgy. 

together  by  a  wire,  a  free  deposit  of  antimony  took  place  in 
twelve  hours. 

Iron  depositing  antimony. — With  iron  in  dilute  hydro- 
chloric acid,  and  antimony  in  a  solution  of  its  chloride,  a 
copious  deposit  of  antimony  was  formed  in  twelve  hours. 

Copper  and  chloride  of  antimony  or  chloride  of  tin. — 
With  copper  in  dilute  hydrochloric  acid,  and  antimony  in 
its  chloride,  or  tin  in  chloride  of  tin,  no  deposit  of  antimony 
or  tin  occurred  in  twenty  hours. 

Bismuth  and  chloride  of  antimony. — With  bismuth  in 
dilute  hydrochloric  acid,  and  antimony  in  chloride  of  anti- 
mony, no  deposit  of  the  latter  occurred  in  twenty-four 
hours. 

Zinc  depositing  copper. — With-  zinc  in  dilute  sulphuric 
acid,  and  brass  in  a  solution  of  cupric  sulphate,  copper  was 
deposited. 

Iron  and  chloride  of  tin. — With  iron  in  dilute  hydro- 
chloric acid,  and  tin  in  a  solution  of  its  chloride,  no  deposit 
of  tin  took  place  in  eighteen  hours. 

Tin  depositing  zinc. — With  tin  in  hydrochloric  acid,  and 
zinc  in  a  neutral  solution  of  its  sulphate,  a  deposit  of  zinc 
was  obtained  in  the  metallic  solution. 

Observations  on  class  of  instances  No.  4. — rst,  it  ap- 
pears that  negative  as  well  as  positive  instances  occur  in 
this  arrangement  in  common  with  the  others  ;  2nd,  that 
by  using  suitable  metals  and  liquids,  deposition  may  be 
effected  more  rapidly  by  this  method  than  by  the  preceding 
ones  ;  3rd,  that  the  metal  which  receives  the  deposit  derives 
its  power  from  its  contact  with  the  other  metal  ;  4th, 
that  base  metals  in  strong  acids  have  the  greatest  power  of 
causing  a  deposit  upon  the  other  metals,  and  noble  metals 
the  least ;  5th,  that  the  noble  metals  are  more  readily  de- 
posited than  the  base  ones  ;  and,  6th,  that  thick  and  co- 
herent deposits  may  be  obtained. 

In  all  the  above  instances,  instead  of  using  one  vessel 
divided  into  two  parts  by  a  porous  diaphragm,  it  will  be 


Methods  of  Electro-Deposition.  89 

found  convenient  to  put  one  of  the  liquids  in  an  unglazed 
earthenware  porous  cell,  and  immerse  the  cell  in  the  other 
liquid  (see  Fig.  i,  p.  18).  In  this  case  either  liquid  may  be 
in  the  outer  vessel. 

FIG.  21. 


Method  No.  5. — Deposition  by  a  separate  current,  or 
*  battery  process '  (see  Fig.  21;  also  Fig.  2,  p.  24).  The  next 
class  of  instances  are  those  in  which  any  of  the  foregoing 
arrangements,  except  the  first,  may  be  connected  by  wires 
with  two  pieces  of  similar  metal  immersed  in  a  separate 
liquid.  In  this  class  of  instances,  the  method  or  arrange- 
ment differs  from  the  three  preceding  ones,  simply  by 
the  wire  which  connects  the  two  pieces  of  metal  being  cut 
in  two,  and  its  free  ends  either  immersed  in  a  separate 
liquid,  or  connected  with  two  pieces  of  metal  dipping  into 
that  liquid.  It  is  not  necessary  to  have  the  depositing 
vessel  separate  ;  it  may  even  be  attached  to  the  same  piece 
of  apparatus,  provided  the  liquid  in  it  is  perfectly  separated 
from  the  other  liquids  and  metals.  The  pieces  of  metal  in 
the  separate  liquid,  possess  no  power  of  deposition  of  them- 
selves in  that  liquid  (unless  they  coat  themselves  by  simple 
immersion),  even  if  they  are  connected  together,  but  wholly 
derive  their  power  of  dissolving  and  receiving  a  deposit, 
from  the  other  metals  and  liquids  by  means  of  the  current 
passing  through  the  wires. 


90  The  Art  of  Electro-Metallurgy. 

Compound  depositing  vessels. — In  each  of  the  foregoing 
arrangements  the  deposition  is  limited  to  a  single  vessel,  but 
any  number  of  depositing  vessels  may  be  connected  together 
in  a  series  (see  Fig.  22,  also  Fig.  3,  p.  24)  so  that  solution  of 

the  anode,  and  deposi- 
tion upon  the  cathode, 
may  be  simultaneously 
obtained  in  every  one 
of  them  by  means  of 
the  same  current.  It 
was  at  one  time  ima- 
gined that  this  was  a 
very  economical  pro- 
cess, because  by  this  means,  with  the  aid  of  one  equivalent 
of  electricity,  and  at  the  expense  of  but  one  equivalent,  each 
of  acid  and  zinc,  several  equivalents  of  metal  were  dissolved 
and  deposited;  but  it  was  soon  found  that  the  process  was  ren- 
dered so  slow,  as  to  neutralise  the  other  advantages,  and  this 
arrangement  therefore  is  but  rarely  employed.  This  practical 
result  would  have  been  anticipated  by  anyone  who  could  have 
interpreted  the  chemical  equivalent  of  electrical  energy.  It 
has  been  recently  patented  by  E.  Casselburg  (see  p.  381). 

General  remarks. — In  each  of  the  foregoing  arrangements, 
the  size  or  shape  of  the  containing  vessels,  the  volume  or 
depth  of  the  liquids,  or  the  size  or  positions  of  the  metals, 
have  no  material  impression  upon  the  production  or  non- 
production  of  a  deposit ;  the  temperature,  however,  is  an 
important  condition,  and  in  all  the  experiments  I  have  de- 
scribed, this  was  about  60°  Fahr. 

Practical  points  to  be  observed. — In  practical  working,  ac- 
cording to  any  one  of  these  methods,  it  is  necessary  to  attend 
to  a  number  of  points  based  upon  the  principles  already  given 
in  the  theoretical  division.  We  must  see  that  the  depositing 
liquid  is  really  an  electrolyte,  that  it  has  a  proper  chemical 
composition,  and  contains  the  requisite  amount  of  water,  free 
acid,  free  alkali,  or  is  neutral,  as  the  case  may  be ;  that  it  has 


Practical  Points.  91 

also  the  proper  degree  of  fluidity,  and  is  at  the  right  tempera- 
ture ;  that  the  strength  of  the  electro-motor  is  suitable  ;  that 
the  electrodes  are  of  the  proper  sizes  and  forms  ;  that  all  the 
substances  through  which  the  current  has  to  pass  will  con- 
duct electricity ;  that  all  the  points  of  contact  of  the  wires 
and  screws,  and  the  surfaces  of  the  immersed  metals,  are  well 
cleaned ;  that  the  circuit  is  really  complete  ;  that  the  elec- 
trodes are  in  proper  positions ;  that  the  current  is  passing 
in  the  right  direction  ;  that  the  different  parts  of  the  liquid 
are  maintained  of  uniform  composition  by  stirring,  &c. 

There  are  many  metallic  solutions,  such,  for  instance,  as 
the  anhydrous  terchloride  of  arsenic,  pentachloride  of  anti- 
mony, the  tetrachloride  of  tin,  &c.,  which  do  not  conduct 
electricity,  and  cannot  therefore  be  used  as  electrolytes. 
Some  others  are  unsuitable  from  other  causes  \  for  instance, 
those  containing  nitric  acid  or  a  nitrate,  are  not  usually 
good,  and  sometimes  will  not  yield  a  metallic  deposit  at  all, 
because  of  the  highly- oxidising  character  of  the  liberated 
acid ;  chlorates,  bromates,  and  iodates,  are  also  rarely  used. 
Iodides  are  liable  to  liberate  free  iodine.  Selenates  and 
phosphates,  also,  do  not  usually  form  good  solutions  ;  the 
former  are  apt  to  have  their  selenium  set  free  by  the  de- 
posited hydrogen.  Sulphides  cannot  often  be  employed, 
because  most  of  them  are  insoluble  ;  and  those  which  are 
soluble  have  a  very  offensive  odour,  and  are  decomposed  by 
the  atmosphere.  Aqueous  solutions  of  chlorides,  sulphates, 
and  cyanides,  are  the  most  usually  suitable  liquids ;  fluorides 
and  bromides,  are  also  often  available. 

Methods  of  forming  a  depositing  solution. — There  -are 
two  ways  of  forming  a  depositing  solution,  one  termed  the 
battery  process,  and  the  other  the  chemical  one.  In  making 
a  solution  by  the  former  method,  the  particular  metal  which 
the  liquid  is  to  contain  and  deposit,  is  employed  as  an  anode, 
and  a  current  from  any  suitable  source  passed  through  the 
liquid  by  means  of  it,  until  a  smooth  and  clean  cathode  ot 
suitable  metal,  receives  a  sufficient  and  proper  metallic  de- 


92  The  A  rt  of  Electro-Metallurgy. 

posit.  Some  operators,  in  making  a  solution  by  the  battery 
process,  fill  a  porous  cell  with  the  liquid,  put  the  cathode  in 
it,  and  place  the  porous  cell  in  the  larger  bulk  of  liquid ;  but 
this  is  an  unnecessary  precaution.  The  chemical  method 
consists  in  preparing  the  ingredients  by  chemical  means,  and 
uniting  them  in  the  proper  proportions,  to  form  the  desired 
solution  ;  in  the  use  of  this  method  it  should  always  be  re- 
membered that  freshly-prepared  precipitates  in  a  wet  state, 
usually  dissolve  much  more  quickly,  thr.n  those  which  have 
been  long  prepared,  or  have  become  dry. 

Method  of  using  a  depositing  solution  (see  also  p.  341). — If 
a  solution  contains  a  very  large  excess  of  uncombined  acid,  or 
other  solvent,  metallic  deposition  will  sometimes  not  occur,  es- 
pecially if  the  metal  to  be  deposited  is  a  highly  positive  one ; 
for  instance,  in  a  solution  of  sulphate  of  zinc,  the  presence  of 
a  large  amount  of  free  sulphuric  acid  will  prevent  the  deposi- 
tion of  zinc.  If  on  the  other  hand,  a  depositing  solution  con- 
tains no  free  combining  substance,  deposition  will  either  pro- 
ceed very  slowly,  or  be  entirely  stopped,  in  consequence  of  an 
insoluble  salt  (often  a  non-conducting  one)  being  formed  upon 
the  anode ;  for  instance,  when  an  electric  current  is  sent 
through  two  silver  plates  immersed  in  a  solution  of  the  pure 
double  cyanide  of  silver  and  potassium,  the  dissolving  plate 
becomes  covered  with  a  white  insoluble  layer  of  cyanide  of 
silver,  which  first  impedes,  and  then  stops  the  current. 

If  a  depositing  solution  is  diluted  with  water  to  a  very 
large  extent,  deposition  will  be  greatly  retarded,  but  if,  on  the 
other  hand,  it  contains  a  great  insufficiency  of  water,  crystals 
of  metallic  salt  will  collect  upon  the  anode,  especially  at  its 
lower  part,  and  gradually  stop  the  current.  This  happens 
in  a  saturated  aqueous  solution  of  cupric  sulphate,  containing 
copper  electrodes  and  plenty  of  free  acid. 

It  is  often  a  great  advantage  to  raise  the  temperature  of 
a  depositing  solution,  because  the  strength  of  affinity  of  the 
liberated  negative  elements  for  the  anode,  increases  by  eleva- 
tion of  temperature,  whilst  that  of  the  different  elements  of 


Practical  Points.  93 

the  electrolyte  for  each  other  diminishes.  Rise  of  tempera- 
ture also  increases  the  electric  conductivity  of  an  electrolyte, 
and  decreases  that  of  the  metal  plates  immersed  in  it,  but,  as 
the  latter  are  by  far  the  best  conductors,  the  final  effect  of 
heating  a  depositing  liquid,  is  a  considerable  increase  of  the 
amount  of  current  passing. 

I  have  repeatedly  observed,  that  with  some  solutions 
used  hot  for  depositing,  if  the  cathode  was  immersed  in  the 
liquid  at  60°  Fahr,  and  the  liquid  then  heated,  no  conduction 
or  deposition  occurred  ;  nor  did  it  take  place  if  the  cathode 
was  removed,  washed  in  cold  water,  and  re-immersed.  But 
if  the  liquid  was  first  heated,  and  then  the  cathode  immersed, 
deposition  occurred  freely,  and  the  liquid  might  be  cooled 
down  considerably  without  stopping  the  action.  In  coating 
iron  with  tin  in  some  liquids,  if  the  iron  was  immersed  before 
heating  the  solution,  no  deposition  occurred  even  at  150°  Fahr, 
but  if  the  liquid  was  first  heated,  even  only  to  90°  or  100° 
Fahr.,  deposition  took  place.  I  have  not  examined  whether 
this  was  due  to  what  has  been  termed  '  the  passive  state.' 

Usually  it  is  not  necessary  to  screen  electro-depositing 
solutions  from  the  direct  action  of  light.  In  some  cases, 
however,  light  decomposes  a  liquid,  and  renders  it  unfit  for 
deposition  ;  this  is  the  case  with  a  liquid  formed  by  dissolving 
hyposulphite  of  silver  in  a  solution  of  hyposulphite  of 
sodium  ;  cyanide  of  silver-plating  liquids  are  also  affected, 
and  turn  brown,  by  the  influence  of  light,  but  not  in  such  a 
way  as  to  render  them  unfit  for  depositing  ;  the  light  only 
affects  the  *  free  cyanide  '  in  them. 

The  rapidity  of  deposition  is  affected  by  the  superficial 
area  of  the  electrodes,  the  length  and  transverse  sectional 
area  of  the  intervening  solution,  and  of  the  connecting  wire. 
The  larger  the  immersed  surface  of  the  electrodes,  the  shorter 
the  length,  and  the  greater  the  transverse  section  of  the  solu- 
tion, and  of  the  connecting  wire,  the  more  rapid  is  the  process. 

The  various  other  conditions,  especially  that  of  proper 
density  of  current,  &c.,  necessary  to  be  secured  in  order  to 


94  The  Art  of  Electro-Metalhirgy. 

obtain  a  metallic  deposit,  and  the  desired  quality  of  metal, 
have  been  already  described  in  the  theoretical  section  (see 
also  p.  341). 


DEPOSITION  OF  INDIVIDUAL  METALS. 
CLASS   I.     GASEOUS   METALS. 

HYDROGEN. 

As  THERE  are  many  persons,  students,  electro- platers,  in- 
ventors and  others,  who  wish  to  make  experiments  for  them- 
selves, and  require  to  know  what  has  already  been  done  in 
the  separation  of  particular  metals  by  means  of  electrolysis, 
the  following  abstract  is  given  of  that  portion  of  the  subject. 
i.  Hydrogen. — Electro-chemical  equivalent  weight  =i. 
As  the  separation  of  hydrogen  is  a  very  common  result  in 
electro-metallurgical  operations,  and  this  element  is  con- 
sidered by  most  chemists  to  be  a  metal,  although  a  gaseous 
one,  and  has  been  called  '  hydrogenium '  in  order  to  indicate 
its  metallic  nature,  I  include  it  amongst  the  metals.  Water, 
and  all  acids  may  be  regarded  as  salts  of  hydrogen,  and  this 
element  is  set  free  by  electrolysis  in  many  solutions  which 
contain  water  or  an  acid,  in  some  cases  by  direct  action,  and 
in  others  as  a  secondary  product,  being  in  the  latter  case 
produced  by  the  action  of  more  electro-positive  substances, 
such  as  the  alkali  metals,  liberated  at  the  cathode,  decom- 
posing the  water  or  acid,  taking  the  oxygen,  etc.  to  them- 
selves, and  setting  the  hydrogen  free. 

Deposition  of  hydrogen  by  simple  immersion  process. — 
The  liberation  of  hydrogen  by  contact  of  the  alkali-metals 
with  water,  is  one  of  the  most  familiar  and  striking  pheno- 
mena of  modern  chemistry.  The  metals  of  the  alkaline 
earths  also,  usually  evolve  hydrogen  slowly  from  water,  and 
nearly  all  the  base  metals  also  behave  similarly,  if  the  water  is 
acidulated.  Even  finely-divided  silver,  gold,  and  platinum, 


Deposition  of  Hydrogen.  95 

set  it  free  from  a  hot  concentrated  solution  of  potassic 
cyanide  (H.  St.  C.  Deville). 

Magnesium  liberates  hydrogen  from  water;  and  its  amal- 
gam with  mercury  does  so  with  violence  (C.  N.  Hartley, 
1  Chemical  News,'  vol.  xiv.,  p.  73).  Magnesium  sets  free 
hydrogen  from  water,  especially  if  the  water  contains  com- 
mon salt,  salammoniac,  or  some  acid  (Roussin,  'Chemical 
News,'  vol.  xiv.,  p.  27).  Hydrogen  is  always  evolved,  when 
a  metal  is  precipitated  from  an  aqueous  liquid  by  means  of 
magnesium  (Commaille,  'Chemical  News,'  vol.  xiv.,  p.  196). 
Finely  divided  iron  (but  not  either  cobalt  or  nickel),  de- 
composes water,  slowly  at  16°  C.  but  rapidly  at  ioo°.C. 
and  liberates  hydrogen  (Troost  and  Hautefeuille, '  Chemical 
News,'  vol.  xxxi.,  p.  196). 

I  have  observed,  that  magnesium  does  not  evolve  hydrogen 
in  dilute  hydrofluoric  acid,  and  but  little  in  an  aqueous  solu- 
tion of  chloride  of  potassium :  but  that  it  evolves  it  freely,  in 
a  mixture  of  the  two  liquids.  Similarly  with  the  same  acid, 
and  a  solution  of  potassic  chlorate.  It  did  not  evolve  the 
gas,  in  a  mixture  of  the  same  acid  and  perchlorate  of  potas- 
sium. It  liberated  hydrogen  from  a  mixture  of  the  acid 
and  a  solution  of  bromide  of  potassium,  but  not  from  either 
alone.  Similarly  with  the  same  acid  and  iodide  of  potassium ; 
but  not  in  a  mixture  of  the  acid  and  a  solution  of  potassic 
iodate.  In  a  mixture  of  hydrofluoric  acid  and  a  solution 
of  potassic  sulphate,  magnesium  set  free  hydrogen,  but  not 
in  either  liquid  singly.  According  to  Deville,  even  silver  de- 
posits hydrogen  violently,  and  forms  argentic  iodide  in  liquid 
hydriodic  acid  ('The  Chemist,'  New  Series,  vol.  iv.,  p.  329). 

Deposition  of  hydrogen  by  separate  current  process. — 
Concentrated  hydrochloric  acid  yields  chlorine  at  the  anode, 
and  hydrogen  at  the  cathode,  as  direct  results  of  the  action 
of  the  current  ;  but,  according  to  Bourgoin,  the  oxygen  and 
hydrogen  obtained,  on  passing  an  electric  current  by  means 
of  platinum  plates,  through  distilled  water  acidulated  with 
pure  sulphuric  acid,  are  probably  not  results  of  an  action 
of  the  current  upon  the  water,  nor  even  results  of  the  action 


96  The  A  rt  of  Electro-Metallurgy. 

of  liberated  electrolytic  products  upon  the  water,  but  of  direct 
decomposition  of  a  hydrate  of  sulphuric  acid  (see  <  Tele- 
graphic Journal,'  vol.  i.,  p.  91,  March  15,  1875). 

I  have  electrolysed  on  many  occasions,  pure  dilute  hydro- 
fluoric acid  with  electrodes  of  numerous  metals ;  and  also 
the  extremely  dangerous  liquid,  anhydrous  hydrofluoric  acid, 
with  electrodes  of  palladium,  platinum,  gold,  gas-carbon,  &c. ; 
hydrogen  was  always  deposited  at  the  cathode  ;  the  numer- 
ous other  effects  obtained  with  that  acid,  will  be  found  de- 
scribed under  the  heads  of  the  respective  metals. 

According  to  Brester,  when  nitric  acid  does  not  liberate 
any  hydrogen  gas  at  the  surface  of  a  cathode  of  platinum 
or  charcoal,  by  the  passage  of  an  electric  current,  the  acid 
is  reduced  to  the  state  of  ammonia  ('  Chemical  News,'  vol. 
xviii.,  p.  144).  Bloxam  also,  has  shewn,  that  the  hydro- 
gen evolved  from  a  platinum  cathode  immersed  in  dilute 
nitric  acid,  or  in  a  solution  of  nitrate  of  potassium,  contained 
in  a  porous  cell,  immersed  in  dilute  sulphuric  acid  containing 
the  anode,  converts  a  portion  only  (not  more  than  one-half), 
of  the  nitric  acid  of  either  of  those  liquids,  into  ammonia 
('  Chemical  News,'  vol.  xix.,  p.  289). 

The  electrolysis  of  concentrated  formic  acid  by  plati- 
num electrodes,  yields  carbonic  acid  and  oxygen  at  the 
anode,  but  that  of  dilute  acetic  acid  gives  pure  oxygen  ; 
aqueous  benzoic  acid  yields  oxygen  at  the  anode  and  hy- 
drogen at  the  cathode,  and  the  latter  sometimes  acquires 
a  black  deposit,  which  disappears  on  exposure  to  light;  it  is 
probably  a  hydride  of  platinum.  A  saturated  aqueous  solu- 
tion of  oxalic  acid,  yields  twice  the  bulk  of  gas  at  the  cathode, 
to  that  at  the  anode  ;  the  latter  is  a  mixture  of  two  volumes 
of  carbonic  anhydride,  and  one  of  oxygen.  A  saturated 
solution  of  tartaric  acid,  gives  oxygen  at  the  anode,  and  hy- 
drogen gas  with  hydride  of  platinum  at  the  cathode  (Brester, 
*  Chemical  News/  vol.  xviii.,  p.  145). 

.  Absorption  of  hydrogen  by  electro-deposited  metals. — As 
hydrogen  is  often  deposited  from  a  solution  by  electrolysis, 
simultaneously  with  other  metals,  electro-deposits  frequently 


Deposition  of  Hydrogen.  97 

contain  it.  Various  experimentalists  have  observed  that 
deposits  of  palladium  and  nickel  absorb  it ;  pure  tin  also  in 
a  less  degree  has  the  same  property  ;  but  cadmium,  zinc, 
aluminium,  copper,  lead,  silver,  mercury,  bismuth,  gold,  and 
platinum  (?)  do  not.  The  correctness  of  these  statements, 
however,  depends  largely  upon  the  kind  of  liquid  electrolysed. 
If  a  piece  of  palladium,  nickel,  cobalt,  or  tin,  has  a  wire  of 
aluminium  twisted  round  it,  and  is  then  immersed  for  a  few 
minutes  in  dilute  acid,  it  absorbs  sufficient  hydrogen  to  exert 
a  slightly  reducing  action  upon  a  solution  of  ferri-cyanide  of 
potassium.  According  to  Bottger,  a  palladium  plate  coated 
with  palladium  black,  absorbs  the  hydrogen  more  quickly, 
and  when  taken  from  the  electrolyte,  and  dried  quickly  by 
blotting-paper,  becomes  red  hot  in  the  air  in  a  few  seconds. 
I  have  repeatedly  observed  that  the  steel  blade  of  a  knife, 
or  a  steel  wire,  becomes  much  more  brittle  after  having  been 
made  the  cathode  and  evolved  hydrogen  in  an  electrolyte, 
and  that  this  occurs  not  only  with  a  dilute  acid  but  also  with 
an  alkaline  liquid.  It  is  not  improbable  that  steam  boilers  are 
sometimes  weakened  by  a  similar  absorption  of  hydrogen, 
when  the  water  employed  in  them  is  decomposed  by  the 
iron.  The  explosive  variety  of  antimony  formed  by  electro- 
lysis is  also  said  to  contain  hydrogen. 


CLASS  II.    BRITTLE  NEGATIVE  METALS. 

ARSENIC,   TELLURIUM,   ANTIMONY,    BISMUTH. 

2.    Arsenic. — Elec.-chem.  eq.  =  I?  =  25.    The  com- 

«5 

monest  salts  of  arsenic  are  arsenious  acid,  i.e.  the  common 
white  oxide  known  as  '  arsenic  ; '  arsenic  acid  ;  and  the 
compounds  of  those  two  acids  with  potash  and  soda. 
Metallic  arsenic  itself  is  a  brittle  substance,  and  an  inferior 
conductor  of  electricity.  Arsenious  acid  is  soluble  in  warm 
hydrochloric  acid ;  also  by  heating  it  to  dryness  with  strong 

H 


98  The  A  rt  of  Electro-Metallurgy. 

nitric  acid  it  is  converted  into  arsenic  acid,  which  is  a  de- 
liquescent substance,  readily  soluble  in  water. 

Deposition  of  arsenic  by  simple  immersion  process. — 
This  element  is  easily  deposited  by  the  simple  immersion 
process,  by  dissolving  arsenious  acid  in  warm  and  somewhat 
dilute  hydrochloric  acid,  and  stirring  the  solution  with  a  strip 
of  bright  copper.  This  experiment  is  well  known  in  toxico- 
logical  chemistry  as  being  an  extremely  delicate  test  for 
arsenic,  devised  by  Reinsch.  According  to  Roussin,  from 
solutions  of  arsenic,  magnesium  deposits  arseniuretted  hy- 
drogen, but  no  arsenic  in  the  metallic  state  ('Chemical 
News/  vol.  xiv.,  p.  27). 

Deposition  of  arsenic  by  the  simple  contact  of  another 
metal. — All  the  arsenic  may  very  easily  be  extracted  from 
arseniferous  substances  by  placing  a  solution  of  them  in  a 
platinum  vessel,  and  immersing  in  it  a  piece  of  zinc  in  con- 
tact with  the  vessel ;  the  arsenic  appears  on  the  platinum. 
By  prolonging  the  action  the  whole  of  the  arsenic  is  extracted 
('  Cosmos,'  Second  Series,  vol.  i.,  p.  595  ;  and  *  Chemical 
News,'  vol.  xii.,  p.  3). 

Deposition  of  arsenic  by  separate  current  process. — I  have 
made  many  experiments  of  electrolysis  of  solutions  of  arsenic, 
and  have  obtained  from  the  aqueous  fluoride  small  portions 
of  a  scaly  deposit,  which  appeared  to  exhibit  in  a  feeble 
degree  the  peculiar  explosive  property  of  the  amorphous 
variety  of  electro-deposited  antimony. 

3.  Tellurium.— Elec.-chem.eq.  =  — 9 =43 'o.  Very  little 

has  been  done  in  the  electro- deposition  of  this  metal,  pro- 
bably in  consequence  of  the  great  cost  of  the  substance. 
Ritter  could  only  obtain  a  pulverulent  deposit  of  it  from  its 
solutions  ;  and  both  he  and  Sir  H.  Davy  found  that,  in  elec- 
trolysing water  by  means  of  an  anode  of  this  metal,  the  water 
surrounding  the  anode  acquired  a  purple  colour,  and  pre- 
cipitated a  brown  powder ;  Magnus  shewed  that  this  powder 
was  metallic  tellurium.  I  have  electrolysed  a  pure  solution 


Deposition  of  Antimony.  99 

of  its  chloride  by  means  of  large  and  smooth  platinum  elec- 
trodes and  a  very  feeble  current,  but  obtained  only  a  jet- 
black  deposit,  the  inner  portion  only  of  which  was  adherent ; 
the  anode  was  not  corroded.  I  have  also  electrolysed  pure 
dilute  hydrofluoric  acid  with  an  anode  of  pure  tellurium,  by 
a  current  from  a  single  Smee's  cell,  and  have  obtained  by 
very  slow  action  most  excellent  deposits  of  bright  reguline 
metal,  of  grey  colour,  and  brittle  crystalline  structure. 

4.  Antimony. — Elec-chem.  eq.--— =40-66.      Its  most 

*J 

common  salts  are  the  oxide,  sulphide,  terchloride,  and  po- 
tassic-tartrate  (tartar- emetic).  The  acid  terchloride  is  the 
ordinary  chloride  of  antimony  as  prepared  for  pharmaceuti- 
cal purposes;  it  is  formed  thus. — Take  one  pound  of  black  sul- 
phide of  antimony,  add  to  it  four  pints  of  hydrochloric  acid, 
gently  heat  the  mixture,  until  the  gas  decreases,  then  boil  it 
slowly  down  to  two  pints,  keeping  it  partly  covered  all  the 
time;  cool  it,  filter  it  through  calico,  and  keep  it  in  a  stoppered 
bottle.  It  is  now  a  yellowish  red  liquid  (the  colour  being 
due  to  iron  in  the  sulphide),  of  specific  gravity  about  1-35  to 

''So. 

A  similar  solution  may  be  made  by  the  battery  method  ; 
this  consists  in  passing  an  electric  current  from  several  cells 
through  pure  and  strong  hydrochloric  acid,  by  means  of  a 
large  anode  of  antimony,  until  a  good  deposit  is  obtained 
upon  a  cathode  of  platinum  of  equal  surface  ;  this  solution  is 
nearly  colourless,  nearly  free  from  iron,  and  much  more  pure 
than  the  other.  A  very  good  solution  may  also  be  easily 
made  by  saturating  ten  ounces,  by  measure,  of  strong  hydro- 
chloric acid  with  freshly-precipitated  teroxide  of  antimony. 
(N.B.  Not  that  made  by  oxidising  antimony  by  nitric  acid, 
nor  that  which  has  been  long  exposed  to  the  air.)  Then 
add  about  five  ounces  more  of  the  acid  to  the  clear  por- 
tion and  stir  the  mixture.  About  three  ounces  of  the  oxide 
will  be  required.  An  excellent  solution  may  also  be  made 
by  dissolving  an  avoirdupois  ounce  of  oxychloride  of  anti- 

H  2 


i  oo  The  A  rt  of  Electro-Metallurgy. 

mony  in  five  ounces  of  pure  hydrochloric  acid  of  specif 
gravity  1*12. 

The  acid  chloride  of  antimony  is  an  excellent  conductc 
of  electricity  ;  it  dissolves  the  anode  freely,  yields  plenty  < 
bright  reguline  metal  if  the  battery  power  is  not  too  strong 
and  its  depositing  power  does  not  deteriorate  by  exposure  t 
light  or  air.  It  is  decomposed  more  or  less  readily  by  zin< 
tin,  lead,  iron,  brass,  copper,  and  german-silver,  each  of  whic 
coat  themselves  with  antimony  in  it  by  simple  immersioi 
Articles  immersed  in  it  require  to  be  washed  with  hydrc 
chloric  acid  before  washing  them  with  water,  otherwise  th 
latter  decomposes  the  adhering  film  of  liquid,  and  cover 
the  articles  with  a  white  insoluble  powder. 

The  mixed  chlorides  of  antimony  and  ammonia  form 
very  good  depositing  liquid.  It  may  be  made  either  b 
the  battery  process,  or  by  mixing  two  measures  of  a  saturate^ 
solution  of  sal-ammoniac  with  two  measures  of  hydrochlori 
acid  and  one  measure  of  water,  and  dissolving  antimony  i: 
it  by  means  of  a  large  anode  of  that  metal  and  a  stron 
battery  current,  or  by  simply  mixing  together  equal  measure 
of  a  saturated  solution  of  sal-ammoniac  and  commerce 
chloride  of  antimony.  This  solution  conducts  well,  yield 
plenty  of  metal  of  good  quality,  and  does  not  act  so  strongl 
upon  base  metals  as  chloride  of  antimony  alone,  but  in  othe 
respects  it  is  like  the  chloride. 

The  potassic  tartrate  of  antimony  (tartar-emetic)  is  mos 
conveniently  obtained  by  purchase.  It  is  a  salt  not  ver 
soluble,  it  requires  about  fifteen  times  its  weight  of  water  t 
dissolve  it  ;  its  aqueous  solution  is  a  very  bad  conductor  c 
electricity,  and  is  not  to  be  compared  with  the  chloride  fc 
depositing  purposes ;  even  with  a  very  feeble  electric  currer 
the  deposited  antimony  consists  only  of  a  small  quantity  c 
a  perfectly  black  powder.  On  the  other  hand,  however,  thi 
salt  is  very  freely  soluble  in  a  mixture  of  two  volumes  of  hy 
drochloric  acid  and  one  of  water.  The  solution  may  b 
made  by  mixing  together  about  two  pounds  of  water,  fou 


Deposition  of  Antimony.  TO  I 

ounds  of  hydrochloric  acid,  and  eight  pounds  of  the  potassic 
.rtrate ;  or  a  larger  proportion  of  water  may  be  added  if 
ssired.  This  mixture  forms  an  excellent  one  for  depositing 
itimony  ;  it  is  a  good  conductor  of  electricity,  it  is  not  in- 
ired  by  long-continued  working,  or  exposure  to  light  or  the 
:mosphere  (I  have  deposited  antimony  from  it  constantly 
iring  many  months)  ;  it  will  bear  a  very  strong  current 
ithout  the  deposit  being  caused  to  pass  k- to  the  state  Of  & 
lack  powder ;  it  yields  reguline  me^al  rapidly,  and  in  coat- 
>gs  of  any  desired  thickness  (I  ha\£e  obtained  deposits  Trbm  - 
a  quarter  of  an  inch  thick).  Deposits  of  about  one-twelfth 
•  an  inch  in  thickness  may  be  obtained  in  about  three  days 
id  three  nights  ;  articles  which  are  wet  with  this  solution 
ay  be  washed  clean  in  water  alone,  without  requiring  to  be 
•eviously  washed  with  hydrochloric  acid. 

Deposition  of  antimony  by  simple  immersion  process  (see  also 
77). — Antimony  may  easily  be  deposited  from  an  acid  solu- 
3n  of  its  terchloride  by  the  simple  immersion  process.  In 
iis  way  a  solution  of  chloride  of  antimony  is  used  for  impart- 
g  a  lilac  colour  to  articles  of  brass.  A  large  quantity  of  water 
added  to  a  small  quantity  of  chloride  of  antimony,  which 
tuses  a  dense  white  precipitate  of  oxychloride  of  antimony; 
ie  mixture  is  boiled  until  the  whole  is  nearly  redissolved, 
ore  water  is  added  to  the  solution,  and  again  boiled  in  like 
anner.  After  being  filtered,  this  clear  liquid  is  raised  to  the 
)iling  point,  and  the  articles  of  brass,  previously  cleaned,  are 
imersed  in  it;  they  immediately  deposit  a  film  of  antimony 
'  a  lilac  colour  upon  themselves  by  the  simple  immersion 
•ocess,  and  are  allowed  to  remain  a  greater  or  less  length 
'  time  according  to  the  tint  required.  They  are  then  well 
ished  in  clean  water,  dried  in  hot  sawdust  in  the  usual 
anner,  and  protected  from  alteration  of  colour  by  lacquering, 
srchloride  of  antimony  is  also  used  for  bronzing  gun-barrels. 

Antimony  powder,  deposited  by  simple  immersion  process 
)m  its  chloride  by  means  of  zinc,  is  used  for  imparting  an 
>pearance  of  grey  cast-iron  to  figures  of  plaster-of- Paris. 


1 02  The  A  rt  of  Electro- Metallurgy. 

According  to  Roussin,  magnesium  deposits  antimoniurette 
hydrogen,  but  no  metallic  antimony,  from  solutions  of  ant 
mony  ('  Chemical  News,'  vol.  xiv.,  p.  27).  I  have  observe 
that  crystals  of  silicon  did  not  become  coated  with  antimon 
in  a  solution  of  fluoride  of  antimony  containing  free  hydn 
fluoric  acid ;  that  zinc  deposited  antimony  as  a  black  powd< 
by  simple  immersion  in  a  solution  of  the  mixed  fluorides  < 
antimony  and  'p'otas^ium ;  and  that  the  oxide  of  iron  ws 
rapidly  dissolved  from  a  rusty  iron  wire  in  a  mixture  of  equ; 
measives  bf  ^ludoti'of  terchloride  of  antimony  and  a  sati 
fated  solution  of  sal-ammoniac. 

Watt  coats  copper  with  antimony  by  simple  immersic 
thus  :  Dissolve  one  ounce  of  chloride  of  antimony  in  or 
pint  of  spirit  of  wine,  and  add  hydrochloric  acid  until  tf 
liquid  is  clear.  Immerse  the  clean  article  in  it  during  aboi 
half  an  hour ;  it  receives  a  bright  coating. 

Gold  in  contact  with  antimony,  in  a  solution  of  cold  < 
boiling  salt  of  antimony,  does  not  acquire  a  coating  of  met 
(Raoult,  '  Chemical  Society's  Journal,'  vol.  xi.,  p.  465). 

Deposition  of  antimony  by  separate  current  process  (see  al< 
pp.  81,  87,  89). — In  depositing  antimony  by  the  battery  pr< 
cess,  the  metal  may  be  obtained  not  only  in  a  state  of  loo: 
black  powder,  but  also  in  two  distinctly  different,  coherer 
reguline  conditions,  viz.,  as  a  very  brittle  metal  of 
grey-slate  colour,  and  hard  crystalline  structure;  and  al: 
as  a  highly  lustrous  steel-black  deposit,  of  amorphous  stru 
ture,  and  somewhat  less  hard  than  the  pure  variety ;  whic 
retains  its  colour  and  brightness  without  oxidizing  for  a  loi 
time. 

A  satisfactory  solution  for  obtaining  the  pure  grey  met 
is  composed  of : — 

Distilled  water 12  ounces. 

Tartar-emetic I  ounce. 

Tartaric  acid I       ,, 

Pure  hydrochloric  acid         .         ,         .  \\    ,, 

It  is  not  a  good  conductor,  and  should  be  worked  slow 


Explosive  Antimony.  103 

nth  two  Smee's  elements,  at  such  a  rate  as  to  deposit  about 
me-eighth  of  an  inch  thick  of  the  metal  in  four  weeks. 

Whilst  engaged  in  depositing  antimony  from  an  acid  solu- 
ion  of  the  terchloride  by  the  separate  current  process,  in 
)ctober  1854,  I  observed  a  singular  development  of  heat 
>y  the  deposited  metal  when  scratched  or  rubbed,  and  pub- 
ished  a  brief  account  of  it  in  the  'Philosophical  Magazine'  for 
anuary  1855.  I  afterwards  investigated  the  phenomenon 
nore  fully  \  and  the  following  account,  condensed  from  the 
Transactions  of  the  Royal  Society '  contains  all  the  leading 
icts  relating  to  it. 

The  best  solution  for  forming  the  strongly-thermic 
•ariety  of  deposit  is  composed  of  one  avoirdupois  ounce  of 
eroxide  of  antimony  or  oxychloride  of  antimony,  dissolved 
n  five  or  six  ounces  of  hydrochloric  acid  of  sp.gr.  1-12  ;  or 
t  may  be  made  by  saturating  two  measures  of  hydrochloric 
,cid  with  oxide  or  oxychloride  of  antimony,  and  then  add- 
ng  one  measure  more  of  the  acid. 

If,  instead  of  the  terchloride  solution,  a  solution  of  either 
erbromide  or  teriodide  of  antimony  is  employed,  the  de- 
>osited  coating  possesses  a  similar  property  of  evolving  heat, 
>ut  in  a  much  less  conspicuous  degree,  especially  the  deposit 
romthe  teriodide;  and  if  a  solution  of  fluoride  of  antimony 
s  employed,  the  deposited  metal  is  of  a  grey  colour,  perfectly 
:rystalline,  and  entirely  destitute  of  the  peculiar  heating 
>roperty.  Under  some  circumstances  this  crystalline  variety 
>f  deposit  may  also  be  obtained  by  electrolysis  from  a  weak 
lolution  of  terchloride  of  antimony,  especially  if  the  battery 
)ower  is  very  feeble,  or  the  liquid  is  employed  in  a  dilute  or 
icated  state. 

In  common  with  electro-deposits  generally,  the  inner 
ind  outer  surfaces  of  both  the  black  and  grey  deposits  are  in 
inequal  states  of  cohesive  tension,  frequently  in  so  great  a 
legree  as  to  rend  the  deposit  extensively,  and  raise  it  from 
he  cathode  in  the  form  of  a  curved  sheet,  with  its  concave 
;ide  towards  the  anode.  This  state  of  tension  is  most  mani- 


1 04  The  A  rt  of  Electro-  Metallurgy. 

fest  with  rapidly-formed,  thin  deposits,  especially  upon 
extended  flat  surfaces. 

It  is  worthy  of  notice  that  if  the  speed  of  deposition  was 
gradually  diminished  to  about  0^5  grain  per  square  inch  of 
cathode  per  hour,  when  it  attained  a  certain  degree  of  slow- 
ness (about  07  grain  per  square  inch  per  hour),  the  charac- 
ter of  the  metal  depositing  suddenly  changed  from  the 
amorphous  black  to  the  crystalline  grey  variety  without  ex- 
hibiting the  slightest  gradation  between,  and  the  two  layers 
of  active  and  inactive  metal  might  be  readily  separated  by 
means  of  a  knife.  With  deposits  very  rapidly  formed,  the 
fractured  surface  was  coarse  and  less  black,  and  the  thermic 
change  was  found  to  be  very  strong,  shattering  the  metal 
with  almost  explosive  violence. 

Faint  crackling  sounds  frequently  issued  from  the  depo- 
siting metal,  evidently  caused  in  most  instances  by  the  co- 
hesive action  just  mentioned,  and  in  other  cases  they  were 
due  to  the  sudden  expulsion  of  bubbles  of  gas  from  holes  in 
the  deposited  metal,  especially  with  the  bromide  variety,  or 
by  depositing  upon  an  iron  cathode  in  the  terchloride  solu- 
tion. The  deposit  obtained  in  the  bromide  solution  was 
frequently  perforated  with  holes  all  over  its  surface,  and  had 
the  appearance  of  a  metallic  sponge  caused  by  the  numerous 
bubbles  of  gas.  The  thermic  property  of  the  deposit  from 
the  terchloride  gradually  disappears,  the  substance  in  a 
state  of  powder  loses  its  power  in  six  months  ;  fragments  one- 
sixteenth  of  an  inch  thick  lose  their  power  in  the  course  of 
twelve  months,  whilst  others  a  quarter  of  an  inch  thick  still 
possess  a  portion  of  their  heating  power  at  the  end  of  three 
or  four  years. 

Each  of  the  varieties  of  active  antimony  is  fragile  and 
easily  broken;  that  from  the  iodide  solution  is  extremely  so. 
Thin  pieces,  one-sixteenth  of  an  inch,  of  the  chloride  variety 
may  be  broken  in  the  air  at  60°  Fahr.  without  discharging 
their  heat,  if  broken  with  care;  thicker  pieces  should  be 
broken  under  the  surface  of  cold  water,  by  gentle  blows  with 


Explosive  A  ntimony.  105 

wood,  or  other  substance  not  very  hard.  Very  thin  pieces  may 
with  care  be  reduced  to  fine  powder  in  a  mortar  under  a 
mixture  of  ice  and  water,  and  the  powder  so  produced,  after 
drying  in  a  thin  layer  in  a  slightly  warm  place,  possesses  all 
the  heating  properties  of  the  original  solid  mass. 

Heating  the  chloride  variety  to  212°  Fahr.  for  one  hour 
in  boiling  water,  or  keeping  it  at  a  somewhat  lower  tempera- 
ture (185°  or  190°  Fahr.)  for  a  longer  period  in  an  air-bath, 
causes  it  gradually  to  evolve  its  heat,  and  lose  its  peculiar 
heating  power. 

A  cylindrical  bar  of  the  chloride  variety,  about  half  an 
inch  in  diameter,  formed  upon  a  rod  of  grain  tin  one-eighth 
of  an  inch  thick,  when  changed  by  the  momentary  contact 
of  a  heated  wire,  evolved  sufficient  heat  to  melt  the  tin  com- 
pletely, and  the  tin  ran  out  through  a  crack  in  the  antimony, 
and  remained  liquid  a  short  time. 

By  applying  momentary  heat  .to  the  ends  of  deposits 
formed  upon  heliacal  copper  wires,  the  action  was  gradually 
transmitted  to  the  opposite  ends  at  a  speed  varying  from 
twelve  to  thirty  feet  per  minute,  the  rapidity  of  progress 
depending  chiefly  on  the  absence  of  cooling  influences, 
cracks  in  the  metal,  and  portions  of  grey  crystalline  deposit. 

The  specific  gravity  of  the  active  chloride  variety  varied 
from  5739  to  5*944 ;  but  after  having  been  discharged  sud- 
denly of  its  heat,  its  specific  gravity  varied  from  5748  to 
6-029.  The  specific  gravity  of  the  inactive  or  pure  crystalline 
variety  varied  from  6*369  to  6-673. 

Their  electro-chemical  equivalents,  determined  by  elec- 
trolysing their  solutions  simultaneously  in  the  same  circuit 
with  a  solution  of  sulphate  of  copper,  and  weighing  the 
deposits,  were  42-30  to  43-81  parts  of  the  active  variety,  and 
40-41  to  40-79  parts  of  the  crystalline  kind  for  every  317 
parts  of  copper  deposited  in  the  copper  solution. 

The  peculiar  change  in  the  active  chloride  variety  is 
attended  by  alterations  in  the  colour,  cohesion,  and  fractured 
surfaces  in  the  substance ;  from  a  bright  steel  colour  and 


106  The  Art  of  Electro-Metallurgy. 

glassy  fracture,  it  passes  to  a  dull  grey  colour  and  granular 
fracture,  and  its  cohesive  power  greatly  increases.  These 
changes  occur  whether  the  heat  has  been  evolved  suddenly 
or  very  gradually  by  long  lapse  of  time.  Similar  effects  are 
observed,  but  in  different  degrees,  with  the  bromide  and 
iodide  deposits  ;  straight  bars  of  the  active  chloride  variety 
suddenly  discharged  become  curved  by  the  heat,  the  outer 
side,  or  that  last  deposited,  invariably  becoming  concave ; 
tins  is  similar  to  the  effect  of  annealing  upon  electro- 
deposited  metals  generally. 

The  heat  evolved  by  the  peculiar  change  in  the  chloride 
variety  is  not  due  to  cohesive  action  ;  for  it  has  been  found 
that  the  amounts  of  heat  evolved  by  similar  weights  of  the 
substance  in  a  single  solid  mass,  in  small  pieces  and  in  fine 
powder,  in  a  calorimeter,  were  not  sensibly  different.  Nor 
is  the  heat  due  to  alteration  of  the  specific  heat  of  the  sub- 
stance during  the  change. 

The  temperature  to  which  the  active  chloride  variety  must 
be  raised,  either  locally  or  throughout  its  mass,  to  produce  the 
sudden  discharge,  varies  according  to  several  circumstances, 
but  is  generally  about  200°  or  210°  Fahr.  in  an  air-bath. 
The  discharge  is  not  limited  to  one  particular  temperature, 
but  commences  between  170°  and  190°,  and  gradually 
increases  in  rapidity  by  rise  of  temperature  to  some  point 
about  200°  or  210°  Fahr.,  when  it  attains  its  maximum,  and 
discharges  all  its  remaining  heat  suddenly.  A  rod  of  the 
substance  may  be  gradually  discharged  of  its  heat  at  one 
end,  without  discharging  the  opposite  end,  by  immersing 
that  end  for  one  hour  in  nearly  boiling  water. 

The  total  amount  of  heat  evolved  by  the  sudden  discharge 
of  the  chloride  variety  was  considerable,  and  was  sufficient 
in  most  instances  to  raise  the  temperature  of  an  equal  weight 
of  ordinary  antimony  of  specific  heat  0*0508,  about  650  or 
700  Fahr.  degrees,  and  in  one  instance  705-89  Fahr.  degrees, 
above  the  atmospheric  temperature  (60°  Fahr.)  at  which  it 
was  discharged. 


Explosive  Antimony.  107 

When  the  active  chloride  variety  is  suddenly  discharged 
of  its  heat,  there  is  invariably  evolved  from  it  a  small  quan- 
tity (generally  about  3*5  per  cent.)  of  vapour,  consisting 
almost  entirely  of  terchloride  of  antimony.  This  evolution 
of  vapour  is  not  a  cause  but  an  effect  of  the  heat. 

The  following  are  the  results  of  two  analyses  of  specimens 
of  amorphous  antimony,  obtained  from  an  acid  solution  of 
the  pure  chloride  : — 


No.  i. 

Sb    .  9336 

SbCl3       .         .5-98 
HC1          .        .     0-46 


6-44 


No.  2. 

Sb    .        .        .  93-51 
SbCl3       .        .6-03) 

HC1  .  .    JT2I  j 

9975 


6-24 


The  second  variety  of  active  antimony  may  be  obtained 
as  follows  :  dissolve  one  part  of  teroxide  of  antimony  in  ten 
parts  of  hydrobromic  acid,  of  specific  gravity  about  1-3  ; 
filter  the  solution,  and  electrolyse  it  by  means  of  three 
Smee's  elements,  and  an  anode  of  antimony,  at  a  speed  of 
deposition  of  about  3  to  5  grains  per  square  inch  of  receiving 
surface  per  hour. 

This  variety  is  of  a  lighter  colour  than  that  from  the 
chloride,  and  is  generally  quite  dull  in  aspect.  It  exhibits 
less  of  the  cohesive  cracking  action  than  the  first  kind,  and 
is  less  hard.  Its  specific  gravity  at  60°  Fahr.  varies  from  5*415 
to  5-472. 

By  momentary  contact  of  a  red-hot  wire,  it  exhibited  a 
similar  molecular  and  thermic  change,  but  the  action  did  not 
spread  throughout  the  mass  unless  it  was  previously  raised  to 
a  temperature  of  about  250°  Fahr. ;  if  then  touched  with  the 
wire  it  evolved  all  the  heat  instantly,  with  explosive  violence 
and  projection  of  pieces  of  the  substance.  Scratching  the 
heated  substance  by  a  steel  pointer  did  not  cause  it  to  dis- 
charge its  heat.  Pieces  heated  upon  mercury,  or  melted 
fusible  alloy,  discharged  themselves  suddenly  and  powerfully 
when  the  bath  attained  a  temperature  of  about  320°  Fahr. 


1 08  The  A  rt  of  Electro-Metallurgy. 

By  fusion  in  a  bent  tube  of  refractory  glass,  it  was  found 
to  consist  of  79^52  per  cent  of  metal  and  20-48  per  cent,  of 
volatile  matter — a  colourless,  buttery  substance,  slightly  semi- 
fluid at  60°  Fahr.,  which  doubtless  consisted  of  terbromide 
of  antimony  and  a  little  aqueous  hydrobromic  acid.  Other 
specimens  treated  thus  gave  respectively  18-42  and  20-40 
per  cent,  of  volatile  matter ;  the  two  specimens  being  part 
of  a  single  deposit,  the  first  being  from  the  upper  and  the 
second  from  the  lower  part  of  the  deposit,  as  it  was  sus- 
pended in  the  electrolyte. 

The  electro-chemical  equivalent  of  this  variety  was 
determined  by  depositing  it  simultaneously  by  the  same 
current  with  the  chloride  variety,  and  ascertaining  the 
relative  weights  of  the  two  deposits.  In  two  experiments  of 
this  kind  there  were  obtained  respectively  50-09  and  50-11 
parts  of  this  variety  for  every  42 -5  parts  of  the  active  chloride 
variety,  or  32-2  parts  of  zinc  consumed.  And  in  two  other 
determinations  51-2  and  51*4  parts  of  bromide  deposit  were 
obtained.  Each  of  these  quantities  of  deposit  contained  the 
same  amount  of  metallic  antimony,  viz.  40  parts  or  one-third 
of  an  atomic  weight  ;  the  remainder  being  the  associated 
salt  of  antimony.  These  results  indicate  that  the  pure  metal 
alone  is  deposited  by  the  current. 

The  third  variety  of  heat  giving  electro-deposited  anti- 
mony was  obtained  as  follows  :  Dissolve  one  part  by  weight 
of  teroxide  of  antimony  in  fifteen  parts  of  hydriodic  acid,  of 
specific  gravity  1-25,  and  electrolyse  it  at  a  speed  not  ex- 
ceeding one  grain  per  square  inch  of  cathode  per  hour. 

The  deposit  is  scaly-grey,  dull  in  appearance,  very 
friable,  and  much  less  metallic  in  character  than  either  of 
the  other  kinds,  unless  it  has  been  deposited  with  extreme 
slowness.  The  specific  gravity  of  a  slowly-formed  specimen 
was  5-27.  On  immersing  dry  pieces  in  water  a  hissing 
sound,  as  of  strong  absorption,  occurred,  and  numerous  bub- 
bles of  gas  issued  from  all  parts  of  its  surface  during  a  few 
seconds.  The  tendency  to  evolution  of  hydrogen  gas  in  the 


Explosive  Antimony.  109 

solution  by  this  variety  is  so  great  as  frequently  to  disinte- 
grate the  deposit  completely. 

Pieces  one-ninth  of  an  inch  thick  required  to  be  heated 
upon  mercury  to  338°  Fahr.  before  the  contact  of  a  red-hot 
wire  would  cause  a  discharge  of  heat  ;  it  then  discharged 
but  feebly,  with  evolution  of  red  vapours  of  iodide  of  anti- 
mony. 

By  fusing  the  unchanged  substance  in  a  glass  tube,  it 
yielded  7776  per  cent,  of  metal,  and  a  solid,  red,  easily 
fusible  sublimate,  together  with  a  little  moisture,  evidently 
teriodide  of  antimony,  and  a  little  aqueous  hydriodic  acid. 

Its  electro-chemical  equivalent  was  determined  in  the 
same  way  as  the  previous  kind.  With  slow  action  (o-5 
grain  per  square  inch  of  cathode  per  hour)  50-39  parts  of 
deposit  were  obtained,  and  with  very  slow  action  (o'2  grain 
per  square  inch  per  hour)  48*07  parts  were  obtained  for 
every  42-5  parts  of  deposit  in  the  chloride  solution. 

The  explosive  kind  of  antimony  electro-deposited  from 
the  chloride  solution  has  been  several  times  rediscovered  in 
America  and  other  places  by  different  persons. 

Amorphous  antimony  is  one  of  the  easiest  of  metals  to 
deposit  in  a  firm,  coherent  state.  Its  appearance  when 
deposited  from  the  chloride,  or  from  the  solution  of  the 
potassic-tartrate  in  hydrochloric  acid,  by  means  of  the  cur- 
rent from  two  or  three  of  Smee's  elements  and  an  anode 
of  antimony,  is  very  beautiful,  and  when  deposited  at  a 
proper  speed  it  has  much  the  appearance  of  highly-polished 
steel.  The  process  should  be  continued  until  the  coating  is 
about  one-twelfth  of  an  inch  in  thickness  on  each  side  of  a 
thin  sheet  of  bright  copper,  employed  as  the  cathode :  this 
will  occupy  about  three  days  and  nights  if  the  current  is 
suitably  strong.  The  solution  should  be  stirred  with  a 
rod  of  gutta-percha  each  morning  and  evening  during  the 
action.  Sometimes  a  deposit  explodes  in  the  liquid  during 
its  formation. 

When  the  deposit  is  sufficiently  thick,  transfer  the  coated 


HO  T/te  A  rt  of  Electro-Metallurgy. 

sheet  to  a  wooden  or  gutta-percha  bowl  into  which  a  stream  of 
cold  water  is  freely  running,  and  clean  the  metal  by  first  pouring 
dilute  hydrochloric  acid  over  it,  and  washing  it  in  the  cold 
water  with  the  aid  of  a  soft  brush.  By  bending  the  sheet  of 
metal  very  slowly  in  the  water,  the  antimony  falls  off  in  large 
plates,  which  may  be  broken  into  smaller  pieces  upon  a  con- 
cave surface  of  wood  under  cold  water  by  a  gentle  blow  with 
the  end  of  a  wooden  rod.  Each  fragment  after  washing  and 
drying  (without  the  aid  of  heat)  should  be  wrapped  in  cotton 
wool,  and  kept  in  a  cool  place.  It  gradually,  during  many 
months,  loses,  more  or  less,  its  heating  property  and  bright- 
ness, and  acquires  an  acid  reaction. 

A  singular  phenomenon  sometimes  occurs  in  depositing 
explosive  antimony.  As  the  solution  is  a  very  dense  one, 
if  it  is  rapidly  worked,  the  exhausted  liquid  rises  to  the  top 
and  lies  in  a  layer  upon  the  surface,  and,  if  the  solution  is 
not  occasionally  stirred,  a  film  of  deposited  metal  forms 
around  the  cathode  upon  the  surface  of  the  liquid  in  the 
form  of  a  button  one  and  a  half  inch  in  diameter. 

I  have  frequently  deposited  collections  of  shining  grey 
crystals  of  the  pure  variety  of  antimony  from  a  saturated 
neutral  solution  of  the  fluoride,  by  means  of  a  current  from 
six  Grove's  or  ten  Smee's  elements  ;  also  from  a  d;lute  solu- 
tion containing  free  hydrofluoric  acid,  by  a  current  from  two 
Smee's  cells.  As  these  crystals  have  a  beautiful  appearance 
and  do  not  oxidize,  some  practical  use  might  probably  be 
made  of  them  for  the  purpose  of  ornamentation. 

For  a  full  account  of  the  properties  of  electro-deposited 
antimony  see  '  Phil.  Trans.  Roy.  Soc.'  1857,  1858,  and  1862  ; 
'Chemical  News,'  vol.  viii.,  pp.  257  and  281  ;  also  *  Journal 
of  the  Cherm'cal  Society.' 

Both  the  black  and  red  sulphides  of  antimony  dissolve 
in  hydrosulphate  of  ammonia,  and  the  resulting  solutions 
conduct  very  freely  with  an  antimony  anode,  and  one  Smee's 
element,  but  yield  no  metal  even  with  a  current  from  twenty- 
five  cells  in  series.  Aqueous  solutions,  either  of  caustic 


Deposition  of  Bismuth.  1 1 1 

potash,  tartrate  or  oxalate  of  potassium,  scarcely  conduct 
at  all  with  an  anode  of  antimony,  and  the  current  from  one 
or  two  Smee's  elements.  Cyanide  of  antimony  dissolved  in 
a  solution  of  cyanide  of  potassium  has  been  proposed  as  a 
depositing  solution,  but  I  have  found  a  solution  of  cyanide 
of  potassium  to  be  a  very  bad  conductor  with  an  anode  of 
antimony. 

A  solution  composed  often  litres  of  water,  500  grammes 
of  finely-powdered  sulphide  of  antimony,  and  2000  grammes 
of  carbonate  of  sodium,  dissolved  by  boiling,  filtered  whilst 
hot,  and  electrolysed  at  a  boiling  temperature,  has  also  been 
recommended  (Roseleur's  '  Galvanoplastic  Manipulation,'  p. 
282)  for  depositing  antimony. 

Antimony  used  as  an  anode  in  water  becomes  covered 
with  oxide.  Fused  oxide  of  antimony  yields  antimony  at 
the  cathode,  but  antimonic  acid  is  formed  at  the  ancde,  and 
stops  the  current.  According  to  Faraday,  fused  terchloride  of 
antimony  conducts  badly  and  is  but  little  decomposed.  I 
have  observed  that  electro-deposited  antimony  did  not  spread 
over  the  blackleaded  surface  of  gutta-percha. 

5.  Bismuth. — Elec.-chem.    eq.  =  f^-=  70.    The  com- 

o 

monest  salts  of  bismuth  are  the  basic  nitrate  (pearl  white 
or  mineral  cosmetic),  the  acid  nitrate,  and  the  chloride. 
The  basic  nitrate  is  formed  by  treating  the  acid  nitrate  with 
abundance  of  water ;  it  is  a  white  powder,  soluble  in  nitric 
or  hydrochloric  acid.  The  acid  nitrate  is  made  by  digesting 
the  metal  in  warm  dilute  nitric  acid,  evaporating  and  crystal- 
lising the  solution.  The  chloride  may  be  made  by  dissolv- 
ing bismuth  in  a  mixture  of  four  measures  of  hydrochloric 
acid  and  one  of  nitric  acid,  and  expelling  all  excess  of  acid 
by  evaporation. 

Deposition  of  bismuth  by  simple  immersion  (see  also  p.  77). 
— Magnesium  deposits  pure  metallic  bismuth  from  solutions  of 
bismuth  salts  (Commaille,  *  Chemical  News,'  vol.  xiv.,  p.  188). 
'  To  coat  articles  of  tin  with  bismuth  by  simple  immersion  : 


1 1 2  The  A  rt  of  Electro- Metallurgy. 

dissolve  ten  grains  of  nitrate  of  bismuth  in  a  wine-glass  full 
of  distilled  water,  to  which  two  drops  of  nitric  acid  have  been 
added.  Immerse  the  articles ;  the  bismuth  will  at  once 
begin  to  be  deposited  upon  them  in  very  small,  shining 
plates.' 

Deposition  of  bismuth  by  a  separate  current  (see  also  pp.  82, 
85, 88). — I  have  deposited  this  metal  by  means  of  an  extremely 
feeble  current,  from  a  solution  of  the  nitrate  in  water,  with 
nearly  the  minimum  amount  of  free  acid.  The  metal  was  then 
reguline,  and  appeared  very  beautiful,  white,  with  a  faintly 
pinkish  tint,  and  with  a  fine  silky  lustre,  but  the  coating  was 
rather  thin ;  the  deposit  would  not  spread  over  a  blackleaded 
surface  in  the  liquid.  According  to  some  writers,  such  a 
deposit  is  liable  to  explode  when  struck.  I  have  also  de- 
posited it  from  a  solution  of  iodide  of  bismuth  and  iodide 
of  potassium,  and  obtained  an  extremely  bulky,  jet-black 
powder,  which  contained  iodine  after  persistent  washing,  and 
slowly  oxidized  and  became  greyish  white  in  the  air  after  many 
months. 

Pure  dilute  hydrofluoric  acid,  with  an  anode  of  bismuth, 
and  a  current  from  a  single  Smee's  element,  conducted  very 
badly  indeed,  and  yielded  only  a  black  film  upon  a  copper 
cathode  in  thirty  hours. 

A  cyanide  solution  has  been  recommended  for  depositing 
this  metal,  but  a  bismuth  anode  does  not  dissolve  readily  in 
a  hot  solution  of  cyanide  of  potassium. 

The  current  from  two  Daniell's  cells  passed  through  a 
solution  of  basic  nitrate  of  bismuth,  and  tartrate  of  sodium, 
gave  a  deposit  of  hydrated  peroxide  of  the  metal  upon  an 
anode  of  platinum  (W.  Wernicke,  '  Journal  of  Chemical 
Society,' vol.  ix.,  p.  307;  '  Chemical  News,'  vol.  xxii.,  p.  240). 

Fused  oxide  of  bismuth,  electrolysed  with  copper  elec- 
trodes, deposits  bismuth  upon  the  cathode ;  with  platinum 
electrodes  the  cathode  forms  a  very  fusible  alloy  with  the 
deposited  metal  (P.  Buckhard,  '  Chemical  News/  vol.  xxi., 
p.  238). 


Deposition  of  Noble  Metals.  1 1 3 

According  to  M.  A.  Bertrand,  metallic  bismuth  may  be 
deposited  upon  copper  or  brass  from  a  solution  composed 
of  thirty  grains  (grammes  ?)  of  the  double  chloride  or  bis- 
muth and  ammonium,  dissolved  in  a  litre  of  water  slightly 
acidified  with  hydrochloric  acid,  by  means  of  a  current  from 
a  single  Bunsen's  cell.  He  states  that  antimony  may  be 
deposited  in  a  similar  manner  ('Athenaeum/  April  22,  1876, 
p.  570).  He  recommends  its  use  for  artistic  decorations, 
instead  of  platinum-black. 

CLASS  III.     NOBLE  METALS 

OSMIUM,   RUTHENIUM,    RHODIUM,    IRIDIUM,    PALLADIUM, 
PLATINUM,    GOLD,    SILVER,    MERCURY. 

6.  Osmium. — Elec.-chem.  eq.  =  I-22-  =  33*16.    Scarcely 

anything  has  been  done  in  the  electro-deposition  of  this  metal. 
F.  Wohler  employed  it  as  an  anode  in  the  electrolysis  of 
dilute  sulphuric  acid,  with  a  current  from  two  Bunsen's  cells, 
and  found  it  freely  converted  into  osmic  acid  (Os  O4),  but 
with  a  solution  of  caustic  soda  as  the  electrolyte,  the  liquid 
became  of  a  deep  yellow  colour,  and  metallic  osmium  was  de- 
posited upon  the  cathode  ('Chemical  News/ vol.  xix.,  p.  10.) 
Smee  electrolysed  a  solution  of  osmic  acid,  and  obtained  a 
black  deposit. 

7.  Ruthenium. — Elec.-chem.  eq.  =I^l-2=26-o5.      Ac- 

4 
cording  to  the  same  authority,  ruthenium  behaves  like  osmium. 


8.  Rhodium. — Elec.-chem.eq.  =      -    =  26-07.     Smee 

3 

leposited  this  metal  from  a  solution  of  its  sodio-chloride,  and 
obtained  a  brittle  white  deposit  by  a  current  from  ten  cells  with 
platinum  electrodes  ;  with  a  stronger  current  the  deposit  was 
a  black  powder.  According  to  a  writer  in  Dingler's  'Poly- 
technic Journal,'  electro-deposited  rhodium  (and  indium) 
detonate  when  heated  (see  'Journal  of  Chemical  Society, 


1 14  The  A  rt  of  Electro-Metallurgy. 

vol.  xi.,  p.  1007),  probably  in  consequence  of  their  contain- 
ing hydrogen. 

9.  Iridium. — Elec.-chem.  eq.  =  -£?  =  49*25.        Smee 

4 

states  that  he  has  reduced  this  metal  in  a  bright  reguline  state 
on  a  small  scale.  According  to  F.  Wohler,  osmi-iridium  is 
readily  dissolved  as  an  anode  in  a  solution  of  caustic  soda 
('  Chemical  News/  vol.  xix.,  p.  10). 

10.  Palladium.— Elec.-chem.  eq.  Io6'5  =26-62.     A 

4 

suitable  depositing  solution  may  be  made  by  precipitating  and 
redissolving  chloride  of  palladium  by  an  excess  of  a  solution 
of  potassic  cyanide,  or  by  sufficiently  saturating  a  solution 
of  cyanide  of  potassium  with  the  metal  by  the  battery 
process.  The  solution  dissolves  a  considerable  quantity  of 
the  metal,  and  is  said  to  yield  thick  metallic  deposits  in  a 
white  reguline  state. 

The  ammonio-chloride  is  also  a  good  salt  for  the  purpose, 
and  should  be  worked  with  a  palladium  anode,  and  a 
current  from  two  or  three  cells  ;  the  current  is  a  little  im- 
peded in  this  solution  by  a  bright  golden  yellow  powder 
forming  upon  the  anode.  Palladium  nitrate  is  less  fitted  for 
electro-metallurgy,  because  it  acts  more  freely  upon  base 
metals,  and  is  apt  to  yield  the  metal  as  a  black  powder  ;  it  is 
however  a  good  conductor  of  the  current.  Iodide  of  palla- 
dium dissolved  in  a  solution  of  iodide  of  potassium  is  still 
less  satisfactory.  M.  A.  Bertrand  recommends  a  perfectly 
neutral  solution  of  double  chloride  of  palladium  and  ammo- 
nium, for  electro  deposition  of  palladium,  either  with  or  with- 
out the  use  of  a  battery  ('  Chemical  News,'  vol.  xxxiv.  p.  227). 

Palladium  used  as  an  anode  in  dilute  sulphuric  acid, 
with  a  current  from  two  Bunsen's  cells,  becomes  slowly 
covered  with  an  almost  black  film  of  peroxide  of  palladium 
(Pd  02)  (F.  Wohler,  'Chemical  News/  vol.  xix.,  p.  10). 

T  have  electrolysed  pure  dilute  aqueous  hydrofluoric  acid 
containing  about  30  per  cent,  of  the  anhydrous  acid,  by 
means  of  a  current  from  six  Smee's  elements,  and  a  small  sheet 


Electrolysis  of  Anhydrous  Hydrofluoric  Acid.   1 1 5 

of  palladium  as  anode,  in  a  large  platinum  cup  as  cathode. 
Conduction  was  free,  much  gas  was  evolved  from  each  elec- 
trode, and  there  was  a  strong  odour  of  ozone.  A  dark  red- 
brown  film  quickly  formed  upon  the  anode,  but  did  not  dis- 
solve after  fifteen  hours  of  action;  the  liquid  was  black  by 
being  filled  with  floating  particles  of  metallic  palladium. 
After  six  days'  action  the  anode  was  greatly  corroded.  In 
the  electrolysis  of  aqueous  hydrofluoric  acid,  by  means  of  a 
palladium  anode  and  platinum  cathode,  two  effects  occur : 
First,  the  water  is  decomposed,  oxygen  being  evolved  at  the 
anode  and  hydrogen  at  the  cathode.  Second,  hydrofluoric 
arid  is  decomposed  also,  the  fluorine  uniting  with  the 
anode,  and  the  hydrogen  escaping  at  the  cathode ;  and  the 
stronger  the  acid,  the  less  is  the  proportion  of  the  water 
decomposed  to  that  of  the  acid. 

As  this  process  offered  a  very  likely  means  of  obtaining 
fluorine  itself,  I  electrolysed  pure  anhydrous  hydrofluoric 
acid  on  several  occasions,  with  a  thick  sheet  of  palla- 
dium as  the  anode,  and  the  platinum-containing  vessel  as  the 
cathode.  This  process  was  difficult  and  very  dangerous  ;  in 
each  case  it  was  conducted  in  the  opening  of  a  chimney, 
and  the  platinum  vessel  containing  the  acid  was  immersed  in 
a  large  bulk  of  a  freezing  mixture,  composed  of  ice  and 
chloride  of  calcium.  Notwithstanding  the  low  temperature 
employed,  and  the  vessel  being  closely  covered  by  a  lid  of 
paraffin,  the  acid  volatilised  rapidly,  partly  in  consequence  of 
the  escaping  hydrogen,  and  the  heat  evolved  by  the  passage 
of  the  current.  The  coldness  of  the  vessel  and  the  intense 
attraction  of  the  acid  vapour  for  moisture  caused  drops  of 
water  to  condense  upon  the  lid  of  the  vessel,  and  made  it 
difficult  to  preserve  the  acid  in  a  perfectly  anhydrous  state  ; 
the  lid  was  therefore  made  so  as  to  overhang  the  outer  edge 
of  the  vessel,  and  had  laid  upon  it  a  layer  of  cotton  wool  to 
absorb  the  moisture. 

In  the  three  first  experiments  the  platinum  cup  was 
usually  about  three  and  a  quarter  inches  deep  and  one  and 


1 1 6  The  A  rt  of  Electro-Metallurgy. 

three-quarters  inch  wide,  and  the  whole  of  its  bottom  part 
inside  was  occupied  by  a  shallow  dish  of  paraffin.  The 
battery  consisted  of  from  six  to  thirty  Smee's  elements  ; 
with  twenty  and  upwards  the  conduction  was  copious.  In 
each  experiment,  with  a  strong  current,  the  anode  quickly 
became  coated  with  a  dark,  red-brown,  brittle  crust,  which 
was  of  a  redder  colour  on  the  side  next  the  anode. 
As  the  coating  entirely  covered  the  immersed  part  of  the 
anode,  and  did  not  greatly  diminish  the  current,  either  it  or 
the  acid  in  its  pores  freely  conducted  electricity.  The 
crust  was  scraped  off,  at  intervals  of  half  an  hour  or  an  hour, 
into  a  platinum  dish,  standing  upon  a  heated  slab  of  iron,  in 
order  to  dry  it  quickly,  and  at  once  transferred  to  a  perfectly 
closed  platinum  bottle.  The  heated  dish  should  not  be  at  a 
temperature  much  exceeding  300°  or  400°  Fahr.  In  each 
instance,  some  black  powder  collected  upon  the  cathode  and 
in  the  paraffin  dish,  and  was  found  to  be  metallic  palladium. 

From  the  small  amount  of  deposit  upon  the  cathode, 
and  the  absence  of  colour  in  the  liquid,  after  eleven  hours' 
action,  it  was  evident  the  crust  was  but  little  if  at  all  soluble 
in  the  anhydrous  hydrofluoric  acid  ;  the  crust  found  in  each 
experiment  was  nearly  black  when  dry,  and  shewed  signs  of 
metallic  particles  when  rubbed  between  smooth  surfaces  of 
agate  ;  it  is  probable  that  the  crust  was  partly  decomposed 
by  contact  with  hydrogen  from  the  cathode. 

The  most  perfect  forms  of  experiment  to  exclude  the 
reducing  effect  of  the  hydrogen  were  made  with  a  platinum 
cup  two  and  three-quarters  inches  wide  and  three  and  a 
quarter  inches  deep,  divided  into  two  equal  parts  by  a 
well-fitting,  thin,  vertical  plate  of  paraffin,  extending  to 
within  half  an  inch  of  the  bottom,  and  covered  by  two  half 
circles  of  that  substance.  The  palladium  anode  and  plati- 
num cathode  were  each  about  four  inches  long  and  one  inch 
wide,  and  firmly  fixed  in  slits  in  the  two  halves  of  the  cover. 
With  five  and  a  half  ounces  of  the  perfectly  anhydrous  acid,  and 
a  current  from  twelve  one-pint  Grove's  elements,  the  conduc- 


Electrolysis  of  A  nhydrous  Hydrofluoric  A  cid.   1 1 7 

tion  was  copious,  and  in  five  minutes  the  part  of  the  anode 
in  the  acid  had  acquired  a  deep-brown  colour.  The  electro- 
lysis was  continued  during  five  hours,  the  anode  being  taken 
out  and  scraped  each  half-hour.  The  crust  was  hard,  and  a 
few  sparks  were  produced  on  some  occasions  by  particles  of 
the  hot  crust  being  decomposed  by  the  heat  of  friction  in 
removing  it.  A  hissing  sound  was  heard  during  the  whole 
of  the  electrolysis,  but  the  fume  of  the  acid  prevented  any. 
effervescence  being  seen.  10-46  grains  of  black  powder 
was  found  upon  the  cathode  arid  adjacent  parts  of  the  con- 
taining-vessel  and  partition,  and  yielded  io-ii  grains  of 
metallic  palladium.  The  anode  had  lost  37-90  grains  in 
weight,  and  54*13  grains  of  the  dry  brown  crust  was  obtained. 
1-37  grain  of  the  crust,  gently  heated  in  a  platinum  lid 
under  a  glass  cover,  generated  a  red  heat  in  itself,  emitted 
sparks,  also  a  vapour  which  attacked  glass  powerfully,  and 
left  a  black  powder  weighing  1*14  grain,  which  by  heating  to 
full  redness  evolved  a  pungent  acid  odour,  and  left  about  -87 
grain  of  pinkish  metallic  palladium.  These  numbers  are  in 
the  proportion  of  61*2  parts  of  expelled  substance  for  each 
1 06 '5  parts  of  residual  palladium. 

I  also  found  that  a  palladium  anode  was  very  rapidly 
caused  to  corrode  by  the  passage  of  a  current  from  three  to 
six  Grove's  elements  through  pure  fluoride  of  potassium  in  a 
state  of  fusion  ;  and  finely  divided  palladium  was  found  in 
the  saline  residue. 

I  electrolysed  strong  nitric  acid  by  means  of  a  current 
from  fifty  Smee's  elements,  with  a  palladium  anode  and  a 
platinum  cathode.  Copious  conduction,  and  rapid  decom- 
position of  the  acid,  with  abundant  evolution  of  red  fumes, 
took  place.  Much  gas  was  evolved  from  the  anode,  but 
none  from  the  cathode,  until  after  a  short  time.  The  anode 
was  not  at  first  visibly  corroded,  but  after  half-an- hour's 
action  the  palladium  slowly  dissolved,  forming  a  red  liquid. 
No  deposit  formed  upon  the  cathode,  With  either  strong 
or  partly  diluted  hydrochloric  acid,  instead  of  nitric,  there 


1 1 8  The  A  rt  of  Electro-Metallurgy. 

was  instant  and  rapid  action,  copious  evolution  of  hydrogen 
at  the  platinum  cathode,  and  chlorine  at  the  palladium  anode, 
and  the  latter  dissolved,  forming  a  blood-red  liquid,  and 
there  quickly  appeared  a  black  deposit  of  palladium  upon  the 
cathode.  With  dilute  sulphuric  acid  the  conduction  was 
copious,  and  a  deposit  of  splendid  colour,  red,  purple,  &c. 
formed  upon  the  anode,  but  no  odour  of  ozone  was  evolved 
unless  the  anode  dipped  only  a  very  small  distance  into  the 
liquid.  By  making  the  sheet  of  palladium  the  cathode  for  a 
short  time,  the  now  well-known  phenomenon  of  bending 
by  absorption  of  hydrogen  took  place,  and  on  taking  it  out 
and  bending  it  by  mechanical  means  it  suddenly  evolved 
much  heat. 

ii.    Platinum. — Elec.-chem.   eq.  =  I97  =  49*25.    The 

4 

only  common  salt  of  platinum  is  the  tetrachloride,  made  by 
dissolving  scraps  of  platinum  in  a  hot  mixture  of  one  volume 
of  nitric  acid  and  two  and  a  half  volumes  of  hydrochloric 
acid,  until  the  liquid  acquires  a  deep-red  colour,  and  then 
evaporating  the  solution  nearly  to  dryness,  and  allowing  it  to 
cool  and  solidify ;  it  is  a  deep-red  salt,  very  freely  soluble 
in  water.  The  other  salts  of  platinum  are  usually  made 
from  it. 

There  are  two  names  applied  to  the  electro-deposition 
of  platinum,  viz.  platinising  and  platinating;  by  the  former 
is  usually  meant  its  deposition  as  a  black  powder  or  film, 
and  by  the  latter  its  precipitation  as  white  reguline  metal. 

For  platinising  either  by  simple  immersion,  or  more 
rapidly  by  the  aid  of  a  separate  current  or  battery,  we  may 
use  the  tetrachloride  dissolved  in  water,  containing  one- 
fourth  its  volume  of  nitric  acid,  or  dissolved  in  water  alone. 
Smee  appears  to  have  been  the  first  to  platinise  sheets  of 
silver  for  the  negative  plates  of  voltaic  batteries. 

Deposition  of  platinum  by  simple  immersion  (see  p.  77).— 
Nearly  all  the  common  metals  become  coated  with  platinum 
by  simple  immersion  in  solutions  of  platinum. 


Deposition  of  Platinum.  119 

A  deposit  of  platinum  in  the  reguline  state  is  more  diffi- 
cult to  obtain  than  one  of  either  copper,  silver,  gold  or  nickel. 
Bright  platinum,  but  of  a  dark  colour,  may  be  obtained  upon 
clean  copper  articles  by  immersing  them  in  a  boiling  solution, 
composed  of  100  parts  by  weight  of  distilled  water,  twelve  of 
caustic  soda,  and  ten  of  the  tetrachloride  of  platinum  ;  forty 
parts  of  sodic  carbonate  may  be  substituted  for  the  twelve 
parts  of  caustic  soda. 

Or  add  to  a  strong  solution  of  the  platinum  chloride, 
carbonate  of  soda  in  fine  powder,  until  effervescence  ceases  ; 
then  add  some  glucose,  and  afterwards  as  much  chloride  of 
sodium  as  will  produce  a  whitish  precipitate.  Place  the 
articles  of  copper  or  brass  which  are  to  be  coated  in  a  zinc 
colander,  and  immerse  them  thus  for  a  few  seconds  in  the 
mixture,  which  should  be  at  a  temperature  of  60°  C.  (=140° 
Fahr.)  Then  wash  the  articles,  and  dry  them  in  hot  saw- 
dust (Les  Mondes,  *  The  Chemical  News/  vol.  xix.  p.  226). 
Magnesium  deposits  pure  platinum  from  a  solution  of 
platinic  chloride  (Commaille,  '  Chemical  News/  vol.  xiv.  p. 
1 88).  I  have  observed  that  crystals  of  silicon  did  not 
deposit  platinum  from  a  solution  of  tetrachloride  of  pla- 
tinum. 

Deposition  of  platinum  by  separate  current  (see  pp.  82,  89). 
— Probably  the  best  solution  for  obtaining  thick  reguline  de- 
posits is  that  employed  by  Roseleur,  and  obtained  as  follows. 
Convert  ten  parts  by  weight  of  platinum  into  dry  tetrachloride 
in  the  manner  already  described,  dissolve  it  in  500  parts  of 
distilled  water,  and  filter  if  necessary.  (N.B.  If  there  is  much 
sediment,  the  salt  has  been  dried  either  too  much  or  care- 
lessly.) Dissolve  also  100  parts  of  crystalline  phosphate  of 
ammonia  in  500  parts  of  distilled  water,  and  add  it,  with 
stirring,  to  the  platinum  solution;  this  produces  a  copious 
precipitate ;  then  add  at  once,  with  stirring,  a  previously  pre- 
pared solution  of  500  parts  of  phosphate  of  soda  crystals  in 
1000  parts  of  distilled  water.  Boil  the  mixture  until  the 
odour  of  ammonia  ceases,  and  the  liquid  which  was  pre- 


1 20  The  A  rt  of  Electro-Metallurgy. 

viously  alkaline  begins  to  redden  blue  litmus  paper;  the 
yellow  liquid  will  then  become  colourless,  and  is  fit  for  de- 
positing. This  solution  is  suitable  for  depositing  upon 
copper  or  its  alloys,  but  not  upon  zinc,  tin,  or  lead,  because 
they  decompose  it  or  platinise  themselves  in  it  by  simple 
immersion.  The  liquid  is  used  hot,  and  requires  a  strong 
battery  current.  As  an  anode  of  platinum  would  not  be 
corroded  in  such  a  liquid,  the  solution  will  of  course  be 
gradually  deprived  of  its  metal  by  the  process  of  deposition 
unless  some  of  the  chloride  be  occasionally  added. 

A  solution  made  by  dissolving  the  chloride  of  platinum 
in  one  of  cyanide  of  potassium,  in  the  proportion  of  about 
twenty  pennyweights  of  the  metal  to  one  gallon,  has  also  been 
employed.  It  is  used  warm  with  a  feeble  current,  but  it  also 
has  the  disadvantage  of  not  dissolving  the  anode,  and  there- 
fore requires  a  stronger  electric  current,  as  well  as  renewal  of 
platinum  salt. 

Other  solutions,  composed  of  the  double  chloride  of 
platinum  and  sodium  ;  or  of  this  salt  dissolved  in  a  solution 
of  oxalic  acid,  and  made  strongly  alkaline  by  means  of 
caustic  soda,  have  been  recommended,  but  it  is  difficult  to 
obtain  reguline  white  platinum  from  them. 

Bottger  states  that  for  platinising  he  takes  a  boiling  so- 
lution of  the  ordinary  chloride  of  platinum  and  chloride  of 
ammonium,  to  which  he  adds  a  few  drops  of  solution  of 
ammonia.  The  solution  contains  very  little  metal,  and  re- 
quires to  be  occasionally  supplied  with  fresh  metallic  solution 
('  Pharmaceutical  Journal,'  vol.  iii.  p.  358). 

In  my  experiments,  a  platinum  anode  in  pure  dilute 
hydrofluoric  acid  of  10  per  cent,  was  not  corroded  by  the 
passage  of  a  current  from  either  six  Smee's  or  six  Grove's 
cells  during  many  hours.  Very  free  conduction  took  place  ;  a 
powerful  odour  of  ozone,  and  a  gas  which  re-ignited  a  red-hot 
splint  was  evolved  at  the  anode,  but  no  deposit  of  platinum 
occurred.  A  solution  of  pure  fluoride  of  potassium  gave  pre- 
cisely similar  effects. 


Electrolysis  of  A  nhydrous  Hydrofluoric  A  cid.     1 2 1 

Also  with  a  current  from  twenty-four  pairs  of  magnesium 
and  platinum,  excited  by  a  solution  of  one  and  a  half  ounce 
of  common  salt  dissolved  in  fifty  ounces  of  water,  and  the 
current  passed  through  pure  dilute  hydrofluoric  acid  of  40 
per  cent,  gas  was  evolved  from  both  electrodes  of  platinum, 
but  no  corrosion  of  the  anode  took  place  in  eighteen  hours. 
I  also  electrolysed  pure  hydrofluoric  acid,  containing  80  per 
cent,  of  the  anhydrous  acid,  with  platinum  electrodes  and  a 
current  from  ten  Smee's  cells.  Abundant  conduction  and 
evolution  of  hydrogen  and  ozone  occurred  ;  the  anode  cor- 
roded and  lost  16*58  grains  in  weight  during  thirty- six  hours, 
and  became  covered  with  a  blackish  crust  which  partly  dis- 
solved in  the  liquid  to  a  brownish  solution,  but  no  electro-de- 
posit of  platinum  occurred.  I  further  electrolysed  anhydrous 
hydrofluoric  acid  in  a  similar  way  with  platinum  electrodes 
to  that  described  with  palladium  (D.  116);  with  a  current 
from  forty  Smee's  elements  the  anode  corroded  rapidly, 
but  did  not  dissolve  in  the  liquid ;  it  acquired  a  dark  red- 
brown  crust,  which  rapidly  deliquesced  in  the  air,  and 
formed  a  blood-red  liquid,  also  some  basic  salt,  by  solution 
in  water. 

I  electrolysed  during  sixteen  hours  pure  dilute  hydro- 
fluoric acid  of  30  per  cent,  mixed  with  an  equal  volume  of 
nitric  acid  ;  gases  were  freely  evolved,  but  scarcely  any  plati- 
num dissolved,  and  none  was  deposited.  Also,  when  mixed 
with  an  equal  volume  of  strong  hydrochloric  acid,  hydro- 
gen and  chlorine  were  evolved,  but  in  four  hours  the  anode 
was  but  little  corroded.  When  mixed  with  an  equal 
volume  of  sulrJjuric  acid,  after  many  hours'  action,  the  anode 
corroded  vflgip  slowly.  And  with  much  selenious  acid  dis- 
solved in, jit,  selenium  containing  traces  of  platinum  was 
freely  deposited,  and  gas  was  evolved  as  before.  With 
phosphoric  anhydride  dissolved  in  it,  the  anode  was 
slowly  corroded,  and  gas  was  evolved  (See  '  Philosophical 
Transactions  of  the  Royal  Society,'  1869,  P-  2O°)- 

By  electrolysing  fluoride  of  potassium  or  of  lithium  in  a 


1 2  2  The  A  rt  of  Electro-Metallurgy. 

melted  state,  a  platinum  anode  was  rapidly  dissolved,  and 
the  resulting  salt  of  platinum  simultaneously  decomposed, 
and  its  metal  set  free :  and  by  electrolysing  pure  double 
fluoride  of  hydrogen  and  potassium,  in  a  fused  state,  the 
platinum  anode  was  rapidly  dissolved,  and  imparted  a  colour 
to  the  fused  salt.  The  fused  fluorides  of  silver,  copper,  lead, 
manganese,  uranium,  or  the  fused  silico-fluoride  of  potas- 
sium, electrolysed  by  a  current  from  six  Smee's  elements, 
did  not  corrode  the  platinum  anode. 

12.    Gold.— Elec.-chem.    eq.  =  I^A  =  49'iS-      The 

o 

commonest  salt  of  gold  is  the  terchloride  ;  and  this  is  the  one 
from  which  other  salts  of  the  metal  are  usually  prepared.  In 
addition  to  this  one,  there  have  been  used  for  electro- 
depositing  purposes,  the  oxide,  bromide,  iodide,  sulphite, 
hyposulphite,  cyanide,  and  double  cyanides. 

Finely-divided  gold  is  also  sometimes  employed  in 
electro-metallurgical  operations  ;  it  is  precipitated  by  adding 
a  clear  solution  of  protosulphate  of  iron  (green  vitriol)  to  a 
warm  solution  of  chloride  of  gold,  until  it  ceases  to  produce 
a  cloud.  It  is  a  brown  powder,  which  assumes  the  metallic 
lustre  on  being  burnished.  One  part  of  gold  requires  about 
five  parts  of  the  crystallised  sulphate  to  precipitate  it.  Oxalic 
acid  produces  a  similar  precipitate  of  gold.  A  solution  of 
sulphurous  anhydride  (sulphurous  acid  H2SO3),  or  a  current 
of  the  gas,  also  precipitates  the  gold  completely  as  metal. 
Many  organic  substances,  if  wetted  with  a  solution  of  chloride 
of  gold,  reduce  it  to  metal,  and  hence  one's  fingers,  paper, 
wood,  a  feather,  caHco,  linen,  &c.,  become  stained  of  a  purple 
colour  by  contact  with  the  liquid  and  subsequent  exposure 
to  light. 

Preparation  of  gold  salts. — Terchloride  of  gold  is  formed 
by  dissolving  metallic  gold  in  a  warm  mixture  of  one  measure 
of  nitric  acid,  and  from  two  to  three  measures  of  hydrochloric 
acid ;  the  mixture  is  called  aqua-regia.  The  gold  dissolves 
slowly  with  evolution  of  gas ;  when  it  is  all  dissolved,  eva- 


Preparation  of  Salts  of  Gold.  123 

porate  the  solution  by  gentle  heat,  with  stirring,  until  it  is 
reduced  to  a  small  bulk,  and  solidifies  on  cooling ;  the  residue 
should  be  entirely  soluble  in  water.  If  it  contains  a  white 
substance  which  will  not  dissolve,  it  is  chloride  of  silver, 
derived  from  traces  of  silver  in  the  metal ;  if  there  is  a  small 
amount  of  yellow  or  brown  residue,  some  of  the  salt  has 
been  overheated ;  such  residue  should  be  redissolved  in  a 
little  aqua  regia,  and  evaporated  to  dryness  again.  One 
ounce  of  gold,  if  it  is  in  small  fragments,  or  thin  sheet,  will  re- 
quire about  four  ounces  of  aqua-regia  to  dissolve  it.  Chloride 
of  gold  is  a  yellow  salt  and  dissolves  in  one  and  a  half 
its  weight  of  water.  If  it  is  properly  made  it  contains  one 
atomic  weight  (=196-6  parts)  of  gold  and  three  atomic 
weights  (—106-5  parts)  of  chlorine,  and  its  composition  is 
represented  by  the  formulae  AuCl3.  One  troy  ounce  of  gold 
will  make  i  oz.  164^  grains  of  the  chloride. 

Oxide  of  gold  is  obtained  by  digesting  a  solution  of  the 
chloride  with  an  excess  of  calcined  magnesia,  washing  the 
precipitate  first  with  dilute  nitric  acid,  and  then  with  water 
only  ;  if  caustic  potash  or  soda  be  used  instead  of  magnesia 
the  oxide  is  liable  to  contain  some  of  the  alkali. 

The  terbromide  of  gold  may  be  formed  by  digesting 
oxide  of  gold  in  hydrobromic  acid,  and  evaporating  the 
solution  by  a  gentle  heat,  with  stirring,  until  it  solidifies  on 
cooling. 

The  oxide  of  gold  forms  on  addition  of  aqueous  ammonia 
or  of  solutions  of  carbonate  sulphate,  or  chloride  of  am- 
monia, a  dark  olive-brown  substance,  called  fulminate  of 
gold,  aurate  of  ammonia,  or  ammoniuret  of  gold.  The  same 
substance  is  also  formed  on  adding  ammonia,  or  a  solution 
of  a  salt  of  ammonia,  to  a  solution  of  terchloride  of  gold. 
It  is  an  extremely  dangerous  substance  when  dry,  and  detonates 
with  the  least  friction  or  percussion.  To  form  ammoniuret 
of  gold,  which  is  sometimes  used  in  electro-gilding  baths, 
convert  ten  parts  by  weight  of  gold  into  the  solid  chloride. 
Dissolve  that  salt  in  water,  and  add  to  the  solution  fifty  parts 


1 24  The  Art  of  Electro-Metallurgy. 

by  weight  of  the  strongest  aqueous  ammonia,  and  stir  the 
mixture,  an  abundant  precipitate  of  the  ammoniuret,  other- 
wise called  fulminate  of  gold,  is  produced  in  the  form  of  a 
yellowish  brown  powder.  When  it  has  subsided,  pour  off 
the  supernatant  liquid,  and  fill  up  again  with  water,  and  re- 
peat this  several  times,  until  the  precipitate  no  longer  smells 
of  ammonia.  The  water  contains  a  little  gold,  and  is  reserved 
for  recovery  of  that  metal.  As  the  yellow-brown  precipitate, 
when  in  a  dry  state,  is  highly  explosive,  it  should  never  be 
allowed  to  get  dry,  and  ought  not  to  be  prepared  until  the 
time  of  forming  a  gilding  solution  with  it.  Particles  of  it 
also  should  not  be  allowed  to  dry  upon  the  edges  of  the 
vessels  nor  upon  filters  through  which  the  wash-liquids  have 
been  passed.  To  remove  the  solid  salt  from  articles,  we 
may  dissolve  it  in  a  solution  of  cyanide  of  potassium. 
Freshly  precipitated  wet  oxide  of  gold  dissolves  in  a  solution 
of  caustic  potash,  to  form  aurate  of  potassium ;  the  solution 
is  yellow,  and  may  be  employed  for  electro-gilding. 

Sulphide  of  gold  is  obtained  by  passing  a  current  of  sul- 
phuretted hydrogen  gas  through  a  solution  of  chloride  of 
gold,  as  long  as  a  precipitate  occurs ;  it  is  a  blackish-brown 
powder. 

'  Cyanide  of  gold  is  formed  by  cautiously  adding  a  solu- 
tion of  cyanide  of  potassium  in  six  parts  of  water,  to  a 
neutral  solution  (i.e.  not  containing  any  free  acid)  of  ter- 
chloride  of  gold,  as  long  as  a  yellow  precipitate  settles  down  ; 
if  more  cyanide  of  potassium  is  added  the  precipitate  be- 
comes dirty  yellow,  and  is  more  quickly  deposited ;  a  still 
larger  quantity  renders  it  orange  yellow  and  redissolves  it. 
It  is  a  crystalline  powder,  permanent  in  the  air  ;  by  ignition 
it  is  resolved  into  gold  and  cyanogen  gas ;  it  is  not  decom- 
posed by  sulphuric,  hydrochloric,  or  nitric  acid,  or  by  aqua- 
regia,  unless  freshly  precipitated,  and  then  only  slowly.  It 
is  not  decomposed  by  sulphuretted  hydrogen  ;  hydrosulphate 
of  ammonia  dissolves  it  slowly  but  completely,  forming 
a  colourless  solution,  from  which,  by  the  addition  of  acid, 


Purity  of  Electro-deposited  Gold.  12$ 

sulphide  of  gold  is  precipitated.  It  dissolves  in  aqueous 
solution  of  ammonia,  hyposulphite  of  soda,  or  alkaline 
cyanides,  but  not  in  water,  alcohol,  or  ether.' 

'  Gold  precipitated  from  a  solution  of  chloride  of  gold  by 
protosulphate  of  iron,  dissolves  in  a  boiling  solution  of 
cyanide  of  potassium  ;  a  hot  solution  of  cyanide  of  potassium 
will  also  dissolve  ordinary  metallic  gold  if  air  be  present. 
Both  oxide  of  gold  and  aurate  of  ammonia  dissolve  com- 
pletely in  a  solution  of  cyanide  of  potassium,  and  form  double 
cyanide  of  gold  and  potassium.  Cyanide  of  gold  requires 
twenty-three  parts  of  cyanide  of  potassium  dissolved  in  water 
to  dissolve  it.  For  every  one  part  of  gold  to  be  dissolved 
by  the  battery-process,  six  parts  of  cyanide  of  potassium, 
dissolved  in  two  to  four  times  the  quantity  of  water  at  100° 
Fahr.,  is  required  ;  two  electrodes  of  gold  being  connected 
with  a  suitable  battery,  and  immersed  in  it,  until  the 
required  quantity  of  gold  is  dissolved.'  'The  crystallised 
cyanide  of  gold  and  potassium  dissolves  in  seven  parts  of  cold 
and  in  half  a  part  of  hot  water '  (Himly), '  in  four  parts  of  cold 
and  in  0*8  part  of  hot  water '  (Glassford  and  Napier).  '  It 
dissolves  very  sparingly  in  alcohol.  Its  aqueous  solution  gilds 
copper  and  silver  by  simple  immersion,  especially  if  hot,  and 
the  copper  and  silver  dissolve  in  it.' 

A  gold  anode  was  speedily  dissolved  in  dilute  hydro- 
chloric acid,  or  in  a  saturated  solution  of  chloride  of  harium, 
sodium,  or  ammonium,  by  a  current  from  twelve  Wollaston's 
cells  ;  but  most  rapidly  in  the  sodic  chloride.  It  was  also 
slowly  dissolved  in  a  solution  of  chlorate  of  potassium,  by  a 
current  from  twenty  such  cells  (H.  Bartlett, '  Chemical  News/ 
vol.  xvi.  p.  257).  Runspaden  has  also  shown  that  a  gold 
anode  in  dilute  sulphuric  acid  is  considerably  oxidised,  and  a 
definite  hydrated  oxide  of  gold  formed  ('  Chemical  News,'  vol. 
xx.  p.  179). 

Electro-deposited  gold  is  not  necessarily  pure,  because 
other  metals  are  often  thrown  down  with  it,  in  order  to  obtain 
the  particular  shade  of  colour  required  ;  for  instance,  white 


1 26  The  A  rt  of  Electro-Metallurgy. 

and  green  gold  contain  silver,  red  gold  contains  copper,  and 
pink  gold  contains  both  copper  and  silver. 

Electrolysis  of  fluorides  with  a  gold  anode, — I  electrolysed 
pure,  dilute  hydrofluoric  acid  with  a  gold  anode  and  a  plati- 
num crucible  cathode,  during  many  hours,  with  a  current 
from  six  Smee's  elements.  Conduction  was  copious,  and 
much  gas  was  evolved  from  each  electrode,  and  an  odour  of 
ozone  came  from  the  anode.  In  a  few  hours  the  anode 
became  covered  with  a  red-brown  film,  which  did  not  dissolve 
but  fell  off.  The  liquid  remained  colourless,  and  was  not 
discoloured  by  addition  of  sulphuretted  hydrogen  water  to  it. 
No  deposit  of  gold  occurred  upon  the  cathode.  I  also 
electrolysed  some  stronger  pure  hydrofluoric  acid  with  the 
same  battery  current,  and  also  with  a  current  from  fifty  pairs 
of  magnesium  and  platinum,  excited  by  a  dilute  solution  of 
common  salt,  and  obtained  similar  effects.  The  deposit  upon 
the  anode  appeared  to  be  metal,  because  it  was  insoluble 
in  nitric  acid,  and  looked  Hke  gold  on  being  burnished  with 
agate. 

Pure  anhydrous  hydrofluoric  acid  at  10°  Fahr.  would  not 
transmit  any  current  from  ten  Smee's  elements  and  a  large 
gold  anode  ;  but  with  forty  Smee's  cells,  as  in  the  experiment 
with  palladium  (see  p.  116),  it  conducted  very  feebly,  and,  by 
continuing  the  action  for  one  and  a  half  hour,  the  anode  ac- 
quired a  dark  reddish-brown  film,  and  a  few  crystals,  at  first  of 
a  green  colour,  appeared  upon  its  edges  ;  the  crystals  became 
yellow  and  then  red  by  exposure  to  the  air. 

A  solution  of  pure  fluoride  of  ammonium,  containing  free 
ammonia  and  a  gold  anode,  conducted  freely  the  current 
from  six  Smee  s  elements.  Much  gas  was  evolved  from  the 
anode,  and  a  bright  lemon-coloured  powder,  insoluble  in 
the  liquid,  formed  upon  the  anode.  No  deposit  of  gold 
occurred. 

I  also  electrolysed  pure  fluorides  of  lithium  and  potassium 
in  a  melted  state,  with  a  gold  anode,  and  a  current  from  both 
three  and  six  Grove's  elements.  The  anode  was  very  rapidly 
corroded,  and  metallic  gold  separated. 


Deposition  of  Gold  by  Simple  Immersion.       1 27 

Solutions  for  gilding. — There  are  many  solutions  for 
electro-gilding,  some  being  formed  by  chemical  means,  and 
some  by  the  separate  current  or  battery  process  ;  but  the  best 
for  thick  deposits  are  those  formed  with  pure  cyanide  of 
potassium  and  cyanide  of  gold,  either  by  the  battery  process 
or  by  chemical  means. 

Separate  gilding  solutions  are  kept  for  different  purposes, 
some  for  gilding  by  simple  immersion  process,  and  some  by 
separate  current ;  others  for  gilding  pale,  yellow,  pink,  &c. 
Some  are  employed  cold,  and  others  hot ;  some  for  gilding 
iron,  steel,  and  the  baser  metals  in  general. 

Deposition  of  gold  by  simple  immersion  (see  p.  77). — Acid 
solutions  of  gold  deposit  their  metal  upon  surfaces  of  phos- 
phorus, silver,  mercury,,  copper,  and  nearly  all  the  base  and 
brittle  metals,  by  simple  contact  with  those  substances.  Ac- 
cording to  Commaille,  magnesium  deposits  pure  gold  from  an 
aqueous  solution  of  the  terchlonde.  ('  Chemical  News,'  vol. 
xiv.  p.  1 88).  I  have  observed  that  crystals  of  silicon  did  not 
deposit  gold  from  a  solution  of  its  terchlonde,  but  that  by 
contact  of  the  terchloride  in  aqueous  solution  with  benzine, 
1  petroleum  ether,'  amylene.  and  a  number  of  other  liquid 
hydrocarbons,  films  of  metallic  gold  gradually  separated. 

For  gilding  articles  of  copper,  bronze,  or  brass,  by  sim- 
ple immersion,  the  following  solution  of  Roseleur's  may  be 
used.  Dissolve  800  parts  by  weight  of  pyrophosphate  of 
soda  in  10,000  parts  of  distilled  water,  and  add  eight  parts  of 
strong  hydrocyanic  acid.  Convert  ten  parts  by  weight  of 
gold  into  soluble  dry  chloride,  dissolve  it  in  a  reserved  por- 
tion of  the  water  to  which  nothing  has  yet  been  added,  and 
mix  the  resulting  liquid  with  the  cold  solution  of  pyrophos- 
phate. The  mixture  is  used  hot ;  it  is  yellowish,  but  must 
become  colourless  when  heated ;  if  it  becomes  red,  a  little 
prussic  acid  must  be  added,  with  stirring,  until  the  liquid  is 
colourless.  If  too  much  of  the  acid  is  added  it  will  prevent 
the  articles  becoming  gilded,  and  this  may  be  corrected  by 
adding  a  small  quantity  of  chloride  of  gold  solution.  The 


1 2  8  The  A  rt  of  Electro- Metallurgy. 

articles  to  be  gilded  must  be  previously  dipped  in  a  very  dilute 
solution  of  nitrate  of  mercury ;  and  whilst  being  gilded  they 
must  be  kept  in  continual  motion.  To  gild  most  success- 
fully by  this  process,  the  articles  should  receive  a  first  coating 
of  gold  in  a  nearly-exhausted  solution  of  the  same  kind,  a 
second  in  a  less  exhausted  one,  and  a  third  in  a  more 
freshly-prepared  one,  to  impart  a  proper  colour.  The 
gilding  occupies  only  a  few  seconds  in  each  bath.  To  ob- 
tain '  green  '  and  '  white  '  gilding  in  such  a  liquid,  a  solution 
of  nitrate  of  silver  is  added,  drop  by  drop,  with  stirring, 
until  the  desired  colour  is  obtained  ;  before  gilding  green  or 
white,  it  is  best  to  gild  the  articles  yellow,  then  dip  them 
quickly  in  the  nitrate  of  mercury  solution,  and  then  into  the 
bath  containing  the  nitrate  of  silver. 

Gilding  by  simple  immersion  is  also  employed  for  putting 
an  exceedingly  thin  deposit  of  gold  upon  large  articles  of 
bronze  previous  to  proper  gilding ;  then  with  a  thicker  deposit 
in  a  cyanide  solution  by  the  battery  process.  The  solution  em- 
ployed is  composed  of  180  parts  of  caustic  potash,  twenty  parts 
of  carbonate  of  potash,  and  nine  parts  of  cyanide  of  potas- 
sium, dissolved  in  1000  parts  by  weight  of  water,  in  which 
has  been  previously  dissolved  as  much  chloride  of  gold  as  is 
formed  from  one  part  by  weight  of  the  metal.  The  mixture  is 
used  nearly  at  a  boiling  temperature.  The  articles  to  be 
gilded  do  not  require  to  be  previously  dipped  in  a  mercurial 
solution.  As  the  solution  loses  its  gold,  chloride  of  gold 
must  be  added,  but  after  four  or  five  such  additions  the 
other  salts  must  also  be  added  with  it,  in  the  above  propor- 
tions. The  solution  may  thus  be  kept  in  order  for  any  length 
of  time. 

It  is  possible  to  gild  copper  and  brass  articles  perfectly 
by  simple  immersion,  by  employing  the  artifice  of '  quicking ' 
the  surface  before  each  immersion,  by  dipping  it  alternately 
into  a  solution  of  nitrate  of  mercury  and  into  the  gilding 
liquid  ;  and  this  plan  is  often  adopted  with  large  articles.  It 
is  said  that  copper  may  be  gilded  so  perfectly  by  this  method 


'  Water- Gilding1  Process.  129 

as  to  resist  for  several  hours  the  corrosive  action  of  concen- 
trated acids.  The  secret  of  the  action  is,  that  each  film  of 
mercury,  being  electro-positive  to  the  gold,  dissolves  in  the 
auriferous  solution,  and  deposits  a  film  of  gold  in  its  place 
(see  pp.  77,  80). 

A  solution  for  gilding  by  simple  immersion  was  at  one 
time  extensively  used  by  Messrs.  Elkington.  It  was  prepared 
as  follows  : — Convert  one  part  of  gold  into  terchloride,  and 
expel  all  excess  of  acid ;  dissolve  it  in  a  small  amount  of 
water,  and  add  gradually  to  it  thirty-one  parts  of  acid  car- 
bonate of  potassium  ;  then  mix  the  liquid  with  a  solution  of 
thirty  parts  more  of  the  acid  carbonate  dissolved  in  200  parts 
of  water,  and  boil  the  mixture  for  two  hours.  During  the 
boiling  the  yellow  solution  becomes  green,  and  is  then  ready 
for  use.  The  previously  cleaned  trinkets  of  brass  or  copper 
are  immersed  for  about  half  a  minute  in  the  hot  liquid.  To 
gild  articles  of  german-silver,  silver,  or  platinum,  in  this 
bath,  they  must  be  immersed  in  contact  with  wires  of  copper 
or  of  zinc.  Chlorate  of  potash  is  formed  in  the  solution  by 
the  gilding  process,  and  a  black  powder  is  precipitated,  con- 
taining carbonate  of  copper  and  a  little  purple  of  Cassius 
(see  Miller's  'Chemistry,'  vol.  ii.,  3rd  ed.,  p.  814). 

The  two  following  liquids  have  also  been  used  for  gilding 
by  the  simple  immersion  or  '  water-gilding '  process.  Con- 
vert five  troy  ounces  of  gold  into  chloride  ;  dissolve  it  in 
four  gallons  of  distilled  water,  add  twenty  pounds  of  pure 
bicarbonate  of  potassium,  and  boil  it  during  two  hours.  The 
articles  to  be  gilded  are  immersed  in  the  warm  liquid  from  a 
few  seconds  to  one  minute,  according  to  the  degree  of  quick- 
ness of  the  action.  For  gilding  articles  of  silver :  dissolve  equal 
weights  of  corrosive  sublimate  and  sal-ammoniac  in  nitric 
acid,  add  some  pure  grain  gold  to  it,  evaporate  the  liquid  to 
half  its  bulk  ;  and  apply  it  whilst  hot  to  the  surface  of  the 
silver  article. 

C.  D.  Braun  gilds  zinc,  by  immersing  it  in  a  solution  of 
sulphide  of  gold  dissolved  in  a  solution  of  sulphide  of  ain- 

K 


1 30  The  A  rt  of  Electro-Metallurgy. 

nionium,  excluded  from  the  atmosphere  ('  Chemical  News/ 
vol.  xxix.  p.  230).  W.  Kirchmann  gilds  clean  iron  by  first 
applying  to  it  sodium  amalgam,  which  coats  it  with  mercury. 
He  then  applies  to  the  mercurialised  surface  a  strong  solu- 
tion of  chloride  of  gold  ;  and  finally  heats  the  object  to  red- 
ness in  a  muffle  ('  Chemical  News/  vol.  xxvii.  p.  268). 

Gilding  by  contact  with  zinc. — Joseph  Steele's  patent, 
dated  Aug.  9,  1855.  It  consists  substantially  in  im- 
mersing the  articles  to  be  gilt,  in  connection  with  a  piece  of 
zinc,  in  a  hot  solution,  formed  by  adding  chloride  of  gold  to 
a  solution  of  cyanide  of  potassium.  It  is  not  an  economical 
process,  because  much  of  the  gold  is  deposited  upon  the  zinc. 

Solutions  for  gilding  by  means  of  a  separate  current 
(see  p.  89). — The  electric  current  employed  is  usually  de- 
rived either  from  a  Bunsen's  battery,  or  a  Clamond's  thermo- 
electric pile,  that  from  a  magneto  electric  machine  being 
found  to  be  less  suitable.  Many  solutions  have  been  tried, 
but  none  have  succeeded  like  the  double  cyanide  of  gold 
and  potassium.  They  may  be  formed  either  by  chemical 
methods,  or  by  means  of  the  battery  process. 

A  solution  may  be  formed  by  chemical  means  as  follows. 
Convert  a  weighed  quantity  of  gold  into  solid  chloride,  dis- 
solve it  in  water,  then  add  a  solution  of  cyanide  of  potassium 
to  it  as  long  as,  but  no  longer  than,  it  produces  a  precipitate, 
stirring  the  mixture  on  each  addition,  and  allowing  it  to  sub- 
side. As  it  is  difficult  and  tedious  to  hit  the  exact  neutral 
point,  and  an  excess  of  either  chloride  or  cyanide  causes 
some  gold  to  remain  in  solution,  the  wash-waters  must  be 
carefully  preserved,  and  the  gold  in  them  recovered.  When 
the  neutral  point  is  attained,  allow  the  precipitate  to  subside, 
pour  off  the  clear  liquid,  and  fill  up  with  water  again,  again 
allow  to  subside,  and  so  on  five  or  six  times  ;  then  pour  the 
sediment  into  a  filter,  and  complete  the  washing  by  addi- 
tion of  water,  and  allow  it  to  drain  thoroughly.  The  pre- 
cipitate should  not  be  allowed  to  dry  because  it  is  liable  to 
contain  a  little  fulminate  of  gold,  derived  from  ammonia 


Solutions  for  Gilding.  131 

produced  from  cyanate  of  potash  present  in  the  cyanide.  The 
wet  substance  should  now  be  added  to  a  small  quantity  of 
a  strong  solution  of  cyanide  of  potassium,  and  just  sufficient 
additional  cyanide  of  potassium  added  with  stirring,  to  dis- 
solve the  whole,  a  note  being  kept  of  the  amount  of  cyanide 
consumed.  About  one-fifth  or  one-fourth  more  of  cyanide 
of  potassium  should  now  be  added,  and  dissolved  to  con- 
stitute what  is  termed  '  free  cyanide  ; '  and  sufficient  water 
be  added,  with  stirring,  to  form  a  solution  containing  the  re- 
quisite amount  of  gold  per  gallon.  The  total  amount  of 
cyanide  required  will  depend  upon  the  quality  of  that  salt, 
which  is  very  variable,  and  with  the  freedom  or  otherwise  of 
the  gold  salt  from  an  excess  of  acid.  Instead  of  dissolving 
cyanide  of  gold  in  the  cyanide  of  potassium,  the  oxide,  the 
ammoniuret,  or  even  the  chloride  of  gold  may  be  added, 
and  will  be  converted  into  cyanide  and  dissolve,  if  sufficient 
cyanide  of  potassium  is  present.  But  the  disadvantage  of 
this  method  is,  that  these  salts  of  gold  introduce  impurities 
into  the  liquid;  the  chloride  is  the  most  objectionable,  be- 
cause it  leads  to  the  formation  of  chloride  of  potassium, 
which  interferes  with  the  perfect  working  of  the  solution. 

The  proportions  of  cyanide  of  gold,  cyanide  of  potas- 
sium, and  water,  in  an  electro-gilding  liquid,  may  vary  very 
greatly  without  detriment  to  the  process,  as  will  be  perceived 
from  the  varied  proportions  used  by  different  persons.  A 
very  good  proportion  is  an  ounce  of  gold,  sixteen  ounces  of 
cyanide  of  potassium,  and  one  gallon  (=160  ounces)  of  water, 
or  an  ounce  of  gold  converted  into  cyanide,  seven  or  eight 
ounces  of  cyanide  of  potassium,  and  100  ounces  of  water  ;  or 
four  ounces  of  gold,  thirty- two  ounces  of  cyanide,  and  160 
ounces  of  water.  The  proportion  of  gold  in  solutions  used 
by  the  separate  current  process,  in  large  electro-gilding 
establishments,  varies  as  much  as  from  ten  pennyweights  to 
fifty  troy  ounces  per  gallon.  Moderately  dilute  gilding  solu- 
tions yield  a  better  quality  of  metal,  though  at  a  slower  rate, 
than  stronger  ones. 

K  2 


1 3  2  The  A  rt  of  Electro- Metallurgy. 

Gilding  solution  of  M.  De  Ruoh — '  Dissolve  ten  parts  of 
cyanide  of  potassium  in  i  oo  parts  of  distilled  water  ;  filter 
the  liquid  and  add  one  part  of  cyanide  of  gold,  prepared 
with  care,  well  washed,  and  dried  out  of  the  influence  of 
light ;  keep  the  mixture  in  a  closed  glass  vessel  at  the 
temperature  of  60°  to  77°  Fahr.  for  two  or  three  days,  out  of 
the  presence  of  light,  with  frequent  stirring.' 

Formula  of  M.  J.  L. — *  First,  take  thirty-one  grammes 
(see  p.  381)  and  twenty-five  centigrammes  of  oxide  of  gold, 
five  hectogrammes  of  cyanide  of  potassium,  and  four  litres 
of  water,  and  boil  them  together  half  an  hour.  The  re- 
suiting  solution  must  be  worked  hot,  and  may  be  used  to 
gild  copper,  brass,  and  silver.' 

'  Second,  dissolve  ten  parts  of  ferro-cyanide  of  potassium 
and  one  part  of  dry  terchloride  of  gold  in  100  parts  of  water  ; 
oxide  of  iron  will  be  precipitated.  Boil  the  solution  two  or 
three  hours  in  a  porcelain  or  glass  vessel,  until  a  precipitate 
collects  at  the  bottom,  and  the  supernatant  liquid  is  trans- 
parent, and  of  a  canary-yellow  colour  ;  filter  the  solution  and 
dilute  it  with  three  times  its  volume  of  water.' 

M.  De  Briant 's process. — *  Dissolve  thirty-four  grammes  of 
gold  in  aqua-regia  and  evaporate  the  solution  until  it  becomes 
neutral  chloride  of  gold  ;  then  dissolve  the  chloride  in  four 
kilogrammes  of  warm  water,  and  add  to  it  200  grammes  of 
magnesia  ;  the  gold  is  precipitated.  Filter  and  wash  with 
pure  water,  digest  the  precipitate  in  forty  parts  of  water  mixed 
with  three  parts  of  nitric  acid  to  remove  magnesia,  then 
wash  the  remaining  oxide  of  gold  with  water  until  the 
wash- water  exhibits  no  acid  reaction  with  test-paper.  Next 
dissolve  400  grammes  of  ferro-cyanide  of  potassium  and  100 
grammes  of  caustic  potash  in  four  litres  of  water,  add  the 
oxide  of  gold,  and  boil  the  solution  about  twenty  minutes. 
When  the  gold  is  dissolved  there  remains  a  small  amount  of 
iron  precipitated,  which  may  be  removed  by  filtration,  and  the 
liquid,  of  a  fine  gold  yellow  colour,  is  ready  for  use  ;  it  may 
be  employed  either  hot  or  cold.' 


Solutions  for  Gilding.  133 

M.  BecquereVs  gilding  liquid. — '  Dissolve  one  part  of 
terchloride  of  gold  and  ten  parts  of  ferro-cyanide  of  potas- 
sium in  100  parts  of  water  ;  filter  the  liquid  to  remove  the 
separated  iron ;  add  100  parts  of  a  saturated  solution  of 
ferro-cyanide  of  potassium,  and  dilute  the  mixture  with  once 
or  twice  its  volume  of  water.  In  general  the  tone  of  the 
gilding  varies  according  as  this  solution  is  more  or  less  di- 
luted ;  the  colour  is  most  beautiful  when  the  liquid  is  most 
dilute,  and  most  free  from  iron.  To  make  the  surface  appear 
bright  it  is  sufficient  to  wash  the  article  in  water,  acidulated 
with  sulphuric  acid,  rubbing  it  gently  with  a  piece  of  linen 
cloth.' 

M.  LevoFs  solution  for  gilding  silver. — *  Dissolve  neutral 
chloride  of  gold  in  water,  then  add  an  aqueous  solution  of 
sulpho-cyanide  of  potassium,  until  the  precipitate  first  formed 
is  re-dissolved.  The  liquid  will  retain  a  slightly  acid  reaction ; 
if  it  has  lost  it,  it  must  be  renewed  'by  adding  a  few  drops  of 
hydrochloric  acid.' 

Gilding  liquids  by  M.  Fizeau. — First,  dissolve  one  part  of 
dry  chloride  of  gold  in  160  parts  of  distilled  water  ;  then  add, 
little  by  little,  a  solution  of  carbonate  of  potash  in  distilled 
water,  until  the  liquid  begins  to  become  cloudy.  We  may 
use  this  liquid  immediately.  And,  second  (used  by  M.  Lere- 
bour),  dissolve  one  gramme  of  chloride  of  gold  and  four  of 
hyposulphite  of  soda,  in  one  litre  of  distilled  water.' 

Mr.  Wood's  gilding  solution. — '  Dissolve  four  troy  ounces 
of  cyanide  of  potassium  and  one  of  cyanide  of  gold  in  one 
gallon  of  distilled  water,  and  use  the  solution  at  about 
90°  Fahr.  with  a  current  from  at  least  two  cells.' 

Making  gilding  solutions  by  the  battery  process. — Excellent 
solutions  for  gilding  may  be  made  by  this  method  ;  and  if 
the  quantity  of  liquid  required  is  not  very  large,  this  plan 
is  by  far  the  most  convenient  and  simple  one,  and  is  un- 
attended by  the  risk  of  loss  of  metal,  which  occurs  in  the  pro- 
cesses of  solution  and  precipitation  of  gold  by  chemical 
means.  To  prepare  a  cyanide  gilding  solution  by  this  plan, 


1 34  The  A  rt  of  Electro- Metallurgy. 

simply  dissolve  some  cyanide  of  potassium  in  hot  distilled 
water,  in  an  earthenware  vessel,  in  the  proportion  of  from 
one  to  two  pounds  to  each  gallon.  Immerse  two  large 
electrodes  of  pure  sheet  gold  in  the  liquid,  and  pass  the  cur- 
rent from  about  three  Smee's,  or  two  Daniell's  cells,  stirring 
the  liquid  occasionally,  until  a  clean  and  bright  cathode  of 
german-silver  (substituted  a  short  time  for  the  gold  one)  re- 
ceives a  proper  coating.  The  liquid  should  be  kept  at  a 
temperature  of  about  150°  Fahr.  during  the  process,  by  im- 
mersing the  vessel  containing  it  in  an  outer  vessel  of  hot 
water  with  a  lamp  beneath.  The  quantity  of  gold  dissolved 
from  the  anode  is  ascertained  by  weighing,  and  is  not  of 
material  consequence,  provided  the  deposit  is  good.  In  this 
process  a  portion  of  the  cyanogen  from  the  cyanide  unites 
with  the  gold,  and  leaves  potash  in  the  solution,  and  after 
a  time,  being  exposed  to  the  atmosphere,  absorbs  carbonic 
acid,  and  thus  brings  carbonate  of  potassium  into  the  liquid, 
but  the  presence  of  this  salt  is  not  objectionable.  A  very 
good  gilding  solution  made  by  this  method  consisted  of 
one  gallon  of  water,  one  and  a  half  pound  of  cyanide  of 
potassium,  and  fifty  pennyweights  of  gold. 

Gold  anodes  should  be  suspended  in  the  liquid,  either  by 
gold  wires  protected  by  tubes  of  gutta-percha,  india-rubber, 
or  glass  (see  p.  171),  or  by  means  of  platinum  wires,  because 
the  gold  is  liable  to  be  cut  through  by  electro-chemical 
action  at  the  surface  of  the  liquid. 

Cold  electro-gilding  solutions  for  the  separate  current  process. 
— Gilding  in  cold  solutions  is  usually  employed  in  cases  where 
the  objects  to  be  gilt  are  massive,  such  as  chandeliers,  clocks, 
&c.,  which  would  otherwise  require  large  volumes  of  liquid  to 
be  heated.  Both  bright  and  dead  gilding  in  cold  liquids  is 
practised  in  large  electro-gilding  establishments.  The  arti- 
cles to  be  gilded  are  coated  with  a  film  of  brass  or  copper 
by  electro-depositing  process,  before  gilding  them  in  a  cold 
solution.  With  a  good  solution  the  gilding  is  quickly  effected. 

The  following  is  the  composition  of  cold  gilding  solutions 


Solutions  for  Gilding.  135 

in  general  use,   and  recommended  by  Roseleur  as  giving 
satisfactory  results. 

1st  Solution. 

Distilled  water 1000  parts. 

Aqueous  ammonia  .  .  .  .  .  50  ,, 
Cyanide  of  potassium  of  70  per  cent.  .  30  „ 
Gold 10  ,, 

Convert  the  gold  into  solid  chloride,  dissolve  the  salt  in 
water,  add  the  ammonia  with  stirring;  the  precipitate  is 
aurate  of  ammonia,  and  highly  explosive  (see  p.  123) ;  wash  it 
by  decantation  and  subsequent  filtration  ;  preserve  the  wash- 
waters,  as  they  contain  a  little  gold.  Dissolve  the  cyanide  of 
potassium  in  nearly  the  whole  of  the  water,  add  the  solution 
to  the  aurate  of  ammonia,  and  stir ;  the  aurate  dissolves 
quickly ;  wash  any  residue  of  aurate  into  the  liquid  by  means  of 
the  remainder  of  the  water,  with  the  aid  of  a  feather.  Boil 
the  mixture  about  one  hour  to  expel  excess  of  ammonia. 

As  this  bath  is  liable  to  become  weaker  in  dissolved  gold 
by  the  process  of  gilding,  it  is  replenished  as  follows  :  Con- 
vert some  gold  into  aurate  cf  ammonia,  add  100  parts  of 
water  for  each  ten  parts  of  gold,  and  then  gradually  dissolve 
cyanide  of  potassium  in  the  mixture  until  the  liquid  is 
colourless.  A  little  of  this  latter  mixture  is  added  to  the 
gilding  solution  as  occasion  requires. 

2nd  Solution. 

Distilled  water  .......     1000  parts. 

Ordinary  cyanide  of  potassium    .         .         30  or  40     ,, 
(Or,  Pure  cyanide  of  potassium  .         .         .       20    ,,  ) 
Gold          ...         ,         ...  10     „ 

Convert  the  gold  into  solid  chloride,  and  dissolve  it  in 
200  parts  of  the  water  ;  dissolve  the  cyanide  in  the  remaining 
800  parts  of  water.  Mix  the  solutions  and  filter  if  necessary. 
Boil  the  liquid  a  short  time  before  first  using  it.  To  re- 
plenish the  solution,  add  occasionally,  as  required,  solid 


136  The  A  rt  of  Electro- Metallurgy. 

chloride  of  gold  one  part,  and  pure  cyanide  of  potassium  from 
one  to  one  and  a  half  parts,  each  dissolved  in  a  little  water. 

The  deposit  of  gold  from  these  solutions  is  often  yellow ; 
if  it  is  dark  red  or  black,  it  indicates  either  an  excess  of  gold 
in  the  liquid  or  too  strong  a  current ;  and  if  it  takes  place 
very  slowly  and  is  of  a  grey  colour,  or  if  one  portion  of  a  gilded 
surface  becomes  ungilded,  whilst  that,  nearer  the  anode  is  re- 
ceiving a  deposit,  it  indicates  either  that  the  electric  current  is 
too  weak,  or  the  presence  of  too  much  cyanide  of  potassium. 

'  Solid*  deposition  of  gold. — A  process,  or  branch  of  trade, 
termed  '  solid  depositing '  has  gradually  extended  itself.  It 
consists  in  making  solid  articles  of  gold  and  silver,  by  electro- 
deposition,  upon  gutta-percha  or  other  moulds;  such,  for 
instance,  as  watch  and  clock  faces,  ornamental  snuff-boxes, 
and  other  articles  elaborately  chased  or  engraved,  or  which 
have  very  complex  or  undercut  ornaments  upon  them ;  the 
expense  of  multiplying  these  by  the  electro-process  being  less 
than  by  the  ordinary  means.  Mr.  Alexander  Parkes  took  out 
a  patent  dated  March  1841,  for  a  solution  for  depositing  solid 
articles  in  gold  ;  it  is  formed  thus  : — Dissolve  one  ounce  of 
pure  gold  in  aqua  regia,  and  evaporate  the  solution  to  dryness  ; 
then  add  two  gallons  of  water  and  sixteen  ounces  of  cyanide 
of  potassium,  and  work  the  resulting  liquid  at  a  temperature 
of  about  120°  or  130°  Fahr. 

Gilding  in  hot  solutions  by  separate  current  process. — This 
is  the  best  method  of  gilding  in  the  great  majority  of  cases. 
For  rapid  gilding  of  small  articles  of  silver,  copper,  bronze, 
or  brass,  Roseleur  employs  a  solution  composed  of — 

Distilled  water  ...         .         .         .  1000  parts. 

Crystallised  phosphate  of  sodium         .         .         60     „ 

Bisulphite  of  sodium 10     ,, 

Cyanide  of  potassium  (pure)        ...  I  part 

Gold I     ,, 

The  phosphate  of  sodium  is  dissolved  in  800  parts  of  the 
water  made  hot.  The  bisulphite  of  sodium  and  cvanide  of 


Gilding  in  Hot  Solutions.  137 

potassium  are  dissolved  together  in  100  parts  of  the  water. 
The  gold  is  converted  into  solid  chloride,  and  dissolved  in 
the  remaining  portion  of  water,  and  the  solution  poured 
slowly,  with  constant  stirring,  into  the  cold  one  of  phos- 
phate of  sodium  ;  and  into  this  mixture,  which  is  greenish 
yellow,  is  at  once  poured  the  solution  of  bisulphite  and 
cyanide.  The  entire  liquid  soon  becomes  colourless,  and 
is  then  ready  for  use.  If  the  solution  of  phosphate  is  not 
cold,  some  of  the  gold  is  precipitated  as  a  metallic  powder. 
If  the  articles  to  be  gilded  are  composed  of  iron  or  steel 
and  require  to  be  gilded  directly,  i.e.  without  previously 
coating  them  with  copper  or  brass,  he  employs  a  liquid 
composed  of — 

Distilled  water 1000  parts. 

Phosphate  of  sodium .         .         .         .         .  50     ,, 

Bisulphite  of  sodium \2\  ,, 

Cyanide  of  potassium  (pure)        .  \  part. 

Gold I       „ 

and  prepares  the  bath  in  a  similar  manner. 

These  baths  are  used  at  a  temperature  which  varies  from 
50°  to  80°  C. ;  they  gild  rapidly,  and  the  gilding  only  occupies 
a  few  minutes. 

In  gilding  articles  of  steel,  they  are,  after  previously 
cleaning,  dipped  in  a  very  hot  bath,  with  a  powerful  current 
at  the  commencement,  and  the  current  then  gradually  dimi- 
nished by  raising  the  anode  until  it  is  nearly  out  of  the 
liquid. 

Roseleur  also  employs  a  solution  composed  of — 

Distilled  water 300  parts. 

Cyanide  of  potassium  (pure)         .         .         .         5     ,, 
Gold I  part 

The  gold  is  converted  into  solid  chloride,  and  dissolved 
in  one  portion  of  the  water,  and  the  cyanide  of  potassium  in 
the  other  portion,  and  the  two  solutions  then  mixed. 

This  liquid  may  be  employed  at  almost  any  tempera- 


138  The  Art  of  Electro- Metallurgy. 

ture,  but  is  liable  to  give  a  yellow  deposit  on  the  upper  part 
of  an  article,  and  a  red  one  at  the  bottom  ;  and  even  to  un- 
gild  the  distant  parts,  whilst  the  near  parts  are  receiving 
a  deposit.  Both  these  defects  may,  however,  be  diminished 
by  keeping  the  articles  in  brisk  and  continual  motion. 

Coloured  gilding. — To  obtain  red  gold,  add  to  either  of  the 
foregoing  solutions  a  sufficient  proportion  of  either  of  the 
acetate  of  copper  liquids  (see  pp.  207,  208),  or  we  may  gild  red 
in  an  old  gilding  bath  in  which  a  great  many  copper  articles 
have  been  gilt,  taking  care  to  use  a  strong  electric  current. 
To  obtain  green  or  white  gold,  add  to  one  of  these  baths  a 
sufficiency  of  either  a  dilute  solution  of  argentic  nitrate,  or 
better,  one  of  double  cyanide  of  silver  and  potassium.  To 
obtain  what  is  called  '  pink  '  gold,  the  articles  are  first  gilt 
yellow,  and  then  red,  and  afterwards  a  mere  blush  of  silver 
is  deposited  upon  the  red  in  a  cold  silver  bath ;  they  are 
finally  burnished.  If  the  proper  pink  colour  is  missed,  strip 
off  the  coating  of  silver  and  copper,  by  immersing  the  articles 
during  a  few  seconds  in  a  mixture  of  five  parts  sulphuric  and 
one  of  nitric  acid  (the  yellow  gilding  then  reappears),  and 
try  again. 

To  obtain  a  rich  deep  gilding  from  a  cyanide  liquid,  the 
solution  should  be  strong,  and  the  articles  should  either 
appear  of  a  dark  yellow  or  a  rich  orange  colour,  approaching 
to  brown,  on  coming  out  of  the  liquid ;  then,  on  scratch- 
brushing  them,  they  will  acquire  the  desired  appearance.  A 
very  rich  dead  gilding  may  also  be  obtained  in  a  cyanide 
solution,  by  adding  a  little  wet  aurate  of  ammonia  to  the 
liquid  just  before  gilding.  And  a  bright  clear  yellow  gilding 
may  be  obtained  by  adding  to  an  ordinary  cyanide  gilding 
solution  a  small  quantity  of  caustic  soda.  If  a  deposit  of 
gold  appears  of  a  blackish  colour  when  coming  out  of  the 
liquid,  it  will  not  have  a  satisfactory  appearance  imparted  to 
it  either  by  brushing  or  burnishing. 

Sometimes  a  defective  colour  in  gilding  is  improved  by 
immersing  the  article,  until  its  colour  is  white,  in  a  solution 


Coloured  Gilding.  139 

3f  nitrate  of  mercury,  then  volatilising  the  mercury  by  heat, 
ind  scratch-brushing  the  article.  2nd.  Or  dip  the  article  in 
strong  sulphuric  acid,  then  heat  it  until  white  fumes  are  freely 
evolved,  and  immerse  it  at  once  in  very  dilute  sulphuric 
acid.  3rd.  Or  make  into  a  wet  paste,  with  a  little  water,  a 
mixture  in  powder,  of  two  parts  nitrate  of  potassium,  one  of 
sulphate  of  zinc,  one  of  alum,  and  one  of  common  salt,  and 
smear  the  article  with  a  layer  of  the  paste  ;  then  heat  it  to 
blackness  upon  an  iron  plate,  over  a  clear  fire,  and  plunge  it 
into  water.  By  varying  the  mixture,  different  tints  of  colour 
are  obtained.  4th.  Or  smear  the  article  with  a  thick  magma 
of  powdered  borax  and  water,  heat  it  until  the  borax 
undergoes  igneous  fusion,  and  plunge  it  into  dilute  sulphuric 
acid. 

Copper  or  brass  trinkets,  which  require  the  gold  to  have 
a  dead  appearance  upon  them,  are  dipped  for  a  moment  in  a 
mixture  of  equal  parts  of  sulphuric  and  nitric  acids,  to  which 
a  little  common  salt  is  added. 

The  colour  of  the  deposit  may  also  be  largely  regulated  by 
the  size  of  the  anode.  If  the  anode  dips  but  slightly  into 
the  solution,  and  the  deposit  is  then  of  a  pale  yellow  colour, 
it  will  become  full  yellow  with  deeper  immersion  of  the 
anode,  and  of  a  red  colour  if  the  anode  is  wholly  immersed. 
It  is  also  largely  affected  by  motion  of  the  cathode ;  if  the 
solution  gilds  of  to6  dark  a  colour,  keeping  the  article  in 
motion  will  remedy  the  defect.  The  colour  may  also  be 
greatly  varied  by  depositing  other  metals  with  the  gold.  In 
all  electro-gilding  establishments  alloys  of  gold,  with  silver 
and  copper,  are  deposited,  in  order  to  obtain  the  requisite 
colour,  and  the  general  method  adopted  for  regulating  the 
colour  of  electro-gilding  is  as  follows  : — After  having  pre- 
pared the  solution,  work  it  with  a  large  copper  anode  until 
the  deposited  metal  begins  to  deteriorate  in  colour ;  then 
replace  the  copper  by  a  small  gold  anode.  With  the  copper 
anode  can  be  obtained  a  full  rich  colour,  becoming  deeper 
as  the  temperature  of  the  liquid  is  higher ;  to  produce  a 


140  The  Art  of  Electro-Metallurgy. 

paler  yellow,  use  a  small  gold  anode  with  the  liquid  at  a 
lower  temperature. 

With  cyanide  of  potassium  solutions,  containing  various 
dissolved  metals,  silver  goes  down  first  by  the  electric-current, 
then  silver  plus  gold,  then  gold  alone,  then  gold  and  copper, 
then  copper  alone,  then  copper  plus  zinc.  If  salts  of  lead 
are  added  to  the  gilding  liquid,  lead  will  first  be  precipitated 
alone,  and  then  the  lead  will  cause  the  gold  to  be  deposited 
in  a  bright  condition. 

Necessity  of  free  cyanide  of  potassium. — In  all  cyanide 
gilding  liquids  it  is  necessary  to  add  much  more  cyanide  of 
potassium  solution  than  is  sufficient  to  dissolve  all  the  salt  of 
gold  ;  this  excess  is  termed  '  free  cyanide.'  The  proportion 
of  free  cyanide  employed  by  different  electro-gilders  varies 
somewhat,  but  does  not  exceed  certain  limits,  otherwise  the 
liquid  will  not  work  well ;  from  one-fourth  to  one-half  of 
the  quantity  required  to  dissolve  the  salt  of  gold  is  a  usual 
proportion.  If  too  much  free  cyanide  is  employed  the 
gilding  is  apt  to  assume  what  is  termed  a  '  foxy  '  appearance, 
the  anode  also  is  dissolved  whilst  the  current  is  not  passing, 
and  the  solution  is  more  prone  to  decompose  and  become  of 
a  dark  colour.  The  reason  why  free  cyanide  is  necessary  in 
gilding  operations,  is  because  the  cyanide  liberated  from  its 
gold  at  the  cathode,  requires  some  time  to  get  across  the  solu- 
tion to  the  anode,  and  meanwhile  the  anode  must  be  sup- 
plied with  some,  in  order  to  render  soluble  the  cyanide  of 
gold  formed  upon  it.  The  actual  quantity  of  cyanide  of 
potassium  required,  both  to  dissolve  the  gold  salt,  and  to 
form  free  cyanide,  differs  very  greatly,  because  the  quality  of 
commercial  cyanide  is  very  variable.  The  larger  the  pro- 
portion of  actual  cyanide  present  in  the  salt,  the  smaller 
the  proportion  of  the  salt  necessary  both  to  dissolve  the  gold 
salt  and  to  form  free  cyanide.  It  must  not  be  forgotten 
that  commercial  cyanide  is  liable  to  contain  from  about  30 
to  98  per  cent,  of  actual  cyanide,  and  that  all  the  other  salts 
in  it  are  almost  useless  as  solvents  of  gold,  and  some  of 


Management  of  Gilding  Solutions.  141 

them  are  positively  detrimental  to  electro-gilding  opera- 
tions. 

Management  of  electro-gilding  solutions. — Cyanide  gild- 
ing solution  is  generally  contained  in  a  glazed  iron  vessel, 
and  heated  either  by  a  stove  or  by  gas-jets  beneath  ;  or  it  is 
contained  in  a  stoneware  or  glass  pan  immersed  in  boiling 
water.  On  account  of  the  usual  smallness  of  the  articles  to 
be  gilded,  the  thinness  of  the  deposit,  and  the  rapidity  of 
the  action  in  a  hot  liquid,  the  objects  only  require  to  be 
immersed  in  the  solution  for  a  few  minutes ;  when  a  thicker 
deposit  is  desired,  in  order  to  maintain  a  proper  condition 
of  deposit,  they  should  be  taken  out  several  times,  brushed, 
and  re-immersed.  The  strength  of  battery  used  for  gilding 
is  generally  about  two  Bunsen's  cells,  of  different  sizes, 
according  to  the  magnitude  of  the  articles  to  be  gilded.  The 
loss  of  water  by  evaporation  is  generally  made  good  by 
adding  a  little  distilled  water,  after  having  finished  gild- 
ing. 

Gilding  done  in  hot  solutions,  is  superior  in  several  re- 
spects to  that  done  in  cold  ones.  The  deposits  are  smoother 
and  cleaner,  and,  what  is  more  important,  the  same  thickness 
of  deposit  is  more  durable  when  made  in  a  hot  liquid  than 
when  effected  in  a  cold  one.  This  may  be  partly  explained 
by  the  fact  that  in  the  subsequent  cooling  the  pores  of  the 
film  of  metal  contract.  Gilding  done  in  hot  solutions  is  also 
generally  more  uniform,  and  of  a  deeper  or  richer  colour 
than  that  done  in  cold  ones. 

Cyanide  gilding  solution  deteriorates  by  long-continued 
working,  in.  consequence  of  silver  getting  into  it  from  the 
anodes,  and  depositing  with  the  gold,  gradually  increasing 
its  paleness  of  colour.  Gold  may  be  obtained  in  a  pure  state 
from  impure  anodes,  &c.  by  dissolving  the  anode  in  mercury 
(seep.  358)  ;  then  immersing  the  amalgam  in  warm  dilute  nitric 
acid  ;  this  will  gradually  dissolve  all  mercury,  silver,  copper, 
and  lead,  and  leave  the  gold  in  a  state  of  fine  metallic  powder. 
Before  adding  the  amalgam  to  the  acid,  the  excess  of  mercury 


T42  The  A  rt  of  Electro-Metallurgy. 

may  be  removed  by  squeezing  it  through  wash-leather,  but  a 
little  of  the  gold  passes  through  also. 

In  all  cyanide  solutions,  and  especially  in  those  contain- 
ing a  large  excess  of  cyanide  of  potassium,  and  exposed  to 
heat  and  sunlight,  a  small  portion  of  the  alkaline  cyanide  is 
continually  being  transformed,  by  contact  with  the  air,  into 
carbonate  of  potassium  and  cyanide  of  ammonium.  To 
remedy  this,  most  electro-gilders  add  occasionally  a  small 
quantity  of  cyanide  of  potassium  to  the  liquid,  others  add  a 
little  hydrocyanic  acid;  the  latteris  rather  themore  suitable, 
because  it  re-converts  the  carbonate  into  cyanide,  but  it  has 
the  disadvantage  of  containing  only  about  5  per  cent,  of  the 
acid,  and  of  being  a  deadly  poisonous  liquid,  and  requiring 
to  be  kept  in  a  dark  and  cool  place. 

Cyanide  gilding  liquids  are  also  liable  to  vary  in  com- 
position, in  consequence  of  the  quantity  of  gold  deposited 
being  sometimes  greater  and  sometimes  less  than  that  dis- 
solved ;  if  it  is  greater,  the  cathode  liberates  an  excess  of  free 
cyanide,  and  if  it  is  less,  the  reverse.  The  gold  anode 
should  always  appear  clean  ;  if  it  has  a  crust  upon  it  there  is 
a  deficiency  of  cyanide,  but  if  it  is  black  and  has  a  slimy 
appearance,  and  especially  if  it  evolves  gas,  the  solution  is 
deficient  of  gold  ;  this  may  be  remedied  by  employing  for  a 
time  a  very  large  anode  and  a  small  receiving  surface.  By 
attending  properly  to  the  indications,  a  cyanide  gilding 
solution  may  be  used  for  any  length  of  time. 

Gilding  base  metals. — Before  gilding  articles  composed  of 
antimony,  lead,  tin  or  zinc,  Britannia  metal,  pewter,  type  metal, 
&c.  it  is  better  to  coat  them  with  a  film  of  copper  or  brass,  in 
a  cyanide  solution,  or  to  begin  the  gilding  in  a  hot  and  nearly 
exhausted  gold  bath,  and  to  carefully  scratch-brush  them. 

A  weaker  solution  is  recommended  for  gilding  articles 
of  iron  or  steel  than  for  gilding  copper,  viz.  one  consisting  of 
about  one  measure  of  the  ordinary  cyanide  gilding  liquid, 
and  four  or  five  measures  of  water  containing  about  i  per  cent, 
of  cyanide  of  potassium.  The  solution  should  only  be 


Gilding  Base  Metals.  143 

moderately  warm,  and  a  feeble  current  employed.  In  gild- 
ing german-silver  or  brass  articles,  also  the  solution  should 
be  weak,  and  a  feeble  current  employed,  because  both  those 
alloys  are  rather  strongly  electro -positive  to  gold  in  a  strong 
cyanide  solution,  and  will  therefore  coat  themselves  by 
simple  immersion  in  it,  and  if  this  action  is  too  strong  it  will 
prevent  the  adhesion  of  the  deposited  metal. 

Previously  prepared  and  cleaned  articles  of  zinc,  are  first 
coated  with  a  thin  film  of  copper  or  brass  in  a  warm  cyanide 
solution,  then  ( scratch- brushed,'  and  a  thicker  coating  of 
copper  put  upon  them  in  a  cold  liquid,  composed  of  a 
mixture  of  ten  volumes  of  water  and  one  of  sulphuric  acid, 
saturated  with  sulphate  of  copper,  and  then  two  or  three 
volumes  more  of  water  added.  If  the  deposit  of  copper 
appears  patchy,  either  the  original  cleaning  process  or  the 
first  coating  of  copper  was  imperfect ;  and  the  articles  must 
be  thoroughly  scratch-brushed,  and-  both  the  coatings  be 
repeated.  The  articles  should  now  be  '  quicked '  by  rapidly 
dipping  them  into  a  solution,  composed  of  distilled  water 
1000  parts,  sulphuric  acid  two  parts,  and  nitrate  of  mercury 
one  part  (see  also  p.  323),  then  rinsed,  and  slightly  silvered 
by  dipping  into  a  mixture  of  water  1000  parts,  cyanide  of  potas- 
sium forty  parts,  and  nitrate  of  silver  ten  parts.  They  are 
then  ready  for  gilding  by  means  of  a  current,  strong  at  first 
so  as  to  cover  the  articles  quickly,  and  then  gradually 
diminished  so  as  to  give  a  good  deposit. 

Gilding  the  insides  of  vessels, — The  insides  of  vessels  are 
gilded,  by  filling  the  vessel  with  the  gilding  solution,  suspend- 
ing a  gold  anode  in  the  liquid,  and  passing  the  current. 
The  lips  of  cream-jugs,  and  the  upper  parts  of  vessels  of 
irregular  outline,  are  gilded  by  passing  the  current  from  a 
gold  anode,  through  a  rag  wetted  with  the  gilding  solution, 
and  laid  upon  the  part. 

Ungilding  of  articles  of  silver  and  iron. — Make  them  the 
anode,  in  a  solution  composed  of  one  part  of  cyanide  of  potas- 
sium dissolved  in  ten  parts  of  water. 


144  The  Art  of  Electro-Metallurgy. 

Recovery  of  gold  from  wash-waters. — Wash-water  from 
gilding  operations,  or  from  the  making  of  salts  of  gold,  should 
never  be  thrown  away  without  previously  testing  it  in  a 
proper  manner.  The  greater  the  quantity  of  free  acid,  alkali, 
or  alkaline  salts,  in  such  a  liquid,  the  more  capable  is  it 
usually  of  dissolving  some  of  the  gold.  All  such  liquids 
have  their  gold  thrown  down  from  them  completely  by 
immersing  in  them  clean  plates  of  zinc,  provided  they  are 
made  slightly  acid,  and  sufficient  time  is  allowed.  Water 
containing  free  chloride  of  gold,  may  be  perfectly  precipitated 
by  means  of  a  solution  of  green  vitriol. 

Recovery  of  gold  from  cyanide  solutions.1 — Add  an  excess 
of  hydrochloric  acid,  carefully  avoiding  the  poisonous 
fumes  of  prussic  acid  j  heat  to  boiling ;  a  yellowish-green 
precipitate  forms,  but  some  gold  still  remains  dissolved ;  cool 
the  liquid,  this  separates  more  of  the  gold.  Decant  or  filter 
the  clear  portion,  heat  the  liquid,  and  add  some  filings  of  zinc; 
in  an  hour  or  two,  all  the  remainder  of  the  gold  will  be  precipi- 
tated. Decant  the  liquid,  boil  the  residue  with  dilute  hydro- 
chloric acid  ;  wash  it  and  add  it  to  the  other  portions. 
Ignite  and  fuse  the  mixture  in  a  platinum  crucible,  with  an 
equal  weight  of  acid  sulphate  of  potassium.  Dissolve  the 
saline  residue  in  boiling  sulphuric  acid,  wash  it  then  with 
water ;  perfectly  pure  gold  will  remain  (R.  Huber,  *  Chemical 
News,'  vol.  viii.  p.  31). 

*  Cyanide  of  gold  and  potassium  gilding  liquid,  when 
mixed  with  sulphuric,  hydrochloric,  or  nitric  acid,  slowly  de- 
posits cyanide  of  gold  ;  and  when  boiled  with  hydrochloric 
acid,  it  is  completely  resolved  into  cyanide  of  gold  and 
chloride  of  potassium.  Similar  effects  are  produced  by  sul- 
phuric or  nitric  acid,  and  even  by  oxalic,  tartaric,  and  acetic 
acids.  When  heated  with  sulphuric  acid  it  gives  off  hydro- 
cyanic acid  gas,  and,  after  ignition,  leaves  a  mixture  of  gold 
and  sulphate  of  potassium.  Iodine  sets  free  cyanogen  gas, 
forms  iodide  of  potassium,  and  throws  down  the  cyanide  of 
gold. 

1  See  also  p.  192. 


Recovering  Gold  and  Silver  from  Old  Solutions.    145 

'  It  we  pour  hydrochloric  acid  into  a  pure  solution  of 
gold  in  cyanide  of  potassium,  there  is  slowly  formed  at 
ordinary  temperatures,  and  immediately  on  the  application 
of  heat,  a  yellow  precipitate,  which  is  cyanide  of  gold  ;  the 
filtered  liquid  which  has  given  this  precipitate  still  contains 
a  little  gold  in  solution.  On  evaporating  the  liquid  to 
dryness,  fusing,  dissolving,  and  filtering  afresh,  there  remains 
upon  the  filter  the  remainder  of  the  gold. 

'  Crystallised  double  cyanide  of  gold  and  potassium  fuses 
and  effervesces  by  heat,  and  is  resolved  into  cyanogen  gas, 
ammonia,  and  cyanide  of  potassium,  if  air  be  present ;  its 
complete  decomposition  requires  a  strong  red  heat.  When 
it  is  strongly  ignited,  mixed  with  an  equal  weight  of  car- 
bonate of  potash,  a  button  of  metallic  gold  is  obtained. 

'  To  obtain  the  remaining  gold  from  gilding  solutions 
which  have  become  inactive,  they  should  be  evaporated  to 
dryness,  the  residue  finely  powdered,  •  and  intimately  mixed 
with  an  equal  weight  of  litharge,  fused  at  a  strong  red  heat, 
and  the  lead  extracted  from  the  alloy  button  of  gold  and 
lead  by  warm  nitric  acid ;  the  gold  will  then  remain  as  a 
loose,  yellowish-brown,  spongy  mass '  (Bottger,  *  J.  Pr. 
Chem.'  xxxvi.  169;  Eisner,  Redtel  Hessenberg,  'J.  Pr. 
Chem.'  xxxvii.  477;  xxxviii.  169,  256). 

Recovering  gold  or  silver,  by  M.  Bolley. — '  Cyanide  of 
gold,  dissolved  in  an  excess  of  cyanide  of  potassium,  resists 
all  the  means  which  we  have  tried  to  separate  them  ;  and 
hydrosulphuric  acid,  for  example,  does  not  produce  a  preci- 
pitate. By  the  wet  way  we  cannot  always  precipitate  the 
gold  completely,  and  for  that  reason  MM.  Bottger,  Hessen- 
berg, Eisner,  and  others,  propose  to  evaporate  the  liquid  to 
dryness  ;  mix  the  residue  with  its  own  weight  of  litharge, 
fuse  the  mixture  at  a  strong  red  heat,  then  dissolve  the  lead 
from  the  alloy  by  boiling  it  a  long  time  with  dilute  nitric 
acid,  which  leaves  the  gold  in  the  form  of  a  light  sponge. 

1  The  following  process  is  applicable  on  the  small  scale, 
with  a  spirit-lamp  and  a  crucible  of  platinum.  Evaporate 

L 


1 46  The  Art  of  Electro- Metallurgy. 

the  solution  to  dryness,  mix  the  saline  mass  with  its  own 
weight  of  sal-ammoniac,  and  heat  it  gently ;  ammoniacal  salts 
decompose,  as  we  have  said,  the  metallic  cyanides,  and  form 
cyanide  of  ammonium,  which  is  itself  decomposed  by  the 
heat  and  volatilised,  whilst  the  acid  of  the  ammoniacal  salt 
(the  body  which  salines  the  ammonia)  combines  with  the 
metals  (passed  to  the  state  of  oxides),  which  were  previously 
united  to  the  cyanogen.  The  sal-ammoniac  then  in  this  case 
forms  chloride  of  potassium  and  chloride  of  gold,  and,  if  the 
salt  contains  ferro-cyanide  of  potassium,  chloride  of  iron  in 
addition.  The  chloride  of  gold  is  easily  decomposed  ;  the 
chloride  of  iron  is  partly  decomposed,  and  leaves  oxide  of 
iron  in  beautiful  crystalline  spangles.  The  undecomposed 
portion  of  the  chloride  of  iron,  like  the  chloride  of  potassium, 
may,  after  the  decomposition  is  finished  (which  only  requires 
a  low  red  heat),  be  washed  away  by  water,  leaving  the 
gold  in  the  form  of  a  light  coherent  mass,  and  the  iron  in 
small  spangles,  which  may  be  removed  by  mechanical  means. 

*  If  we  fear  that  a  little  of  the  gold  remains  mixed  with 
the  iron  in  a  pulverulent  state,  we  may  dissolve  it  in  hot  aqua 
regia,  and  precipitate  the  gold  from  the  resulting  solution  by 
adding  to  it  a  solution  of  protosulphate  of  iron ;  but  this 
appears  superfluous  ;  and  I  am  assured,  by  evaporation  of 
given  volumes  of  the  same  solution  of  gold,  the  evaporation 
and  calcination  of  the  sal-ammoniac,  and  other  operations, 
that  we  have  collected  in  a  sufficiently  exact  manner  all  the 
gold  of  these  solutions. 

'  The  same  process  is  applicable  to  the  solution  of  silver, 
and,  independently  of  the  oxide  of  iron  (of  the  ferro-cyanide 
of  potassium),  we  obtain  chloride  of  silver,  which  is  soluble 
in  aqueous  ammonia.' 

13.  Silver. — Elec.  chem.  eqt=io8.  As  silver  is  the  most 
prominent  metal  in  electro-depositing  processes,  I  shall  speak 
of  it  the  most  fully.  The  commonest  salts  of  silver  are  the 
chloride,  nitrate,  oxide,  cyanide,  and  sulphide  ;  the  sulphite, 
hyposulphite,  acetate,  and  other  salts  have  however  been 


Making  Salts  of  Silver.  147 

tried  for  electro-plating  purposes,  but  the  one  which  has  best 
stood  the  test  of  experience  and  time  is  the  double  cyanide 
of  silver  and  potassium. 

Most  of  the  salts  of  silver  are  formed  from  the  nitrate. 
The  nitrate  is  produced  by  adding  pure  grain  silver,  in  small 
quantities  at  a  time,  to  a  warm  mixture  of  one  measure  of 
distilled  water  and  four  measures  of  the  purest  and  strongest 
nitric  acid.  If  the  liquid  is  too  hot,  or  too  much  silver  is 
added  at  a  time,  the  action  will  be  very  strong,  and  loss  of 
materials,  by  boiling  over  of  the  liquid,  may  be  occasioned  ; 
in  such  a  case  add  a  small  quantity  of  cold  distilled  water. 
When  the  liquid  ceases  to  dissolve  more  metal,  it  should  be 
evaporated  and  crystallised,  or  else  kept  in  a  covered  vessel, 
protected  from  the  light  until  required  to  be  used. 

The  oxide  is  obtained  by  adding  a  solution  of  either 
caustic  potash,  causiic  soda,  or  clear  lime-water,  to  one  of 
nitrate  of  silver  as  long  as  it  produces  a  precipitate,  filtering 
and  washing  the  oxide,  which  is  a  brown  powder.  The  wash- 
water  contains  a  little  oxide  of  silver  in  a  dissolved  state. 
The  chloride  may  be  obtained  by  adding  dilute  hydrochloric 
acid  or  a  solution  of  common  salt,  in  slight  excess,  to  one  of 
the  nitrate  in  a  similai  manner,  filtering  and  washing  the 
white  flocculent  precipitate,  which  must  be  kept  in  the  dark. 
In  this  case  the  wash-waters  do  not  contain  silver,  and  may 
therefore  be  thrown  away. 

Fluoride  of  silver  may  be  obtained  by  saturating  pure  di- 
lute hydrofluoric  acid  in  a  platinum  vessel  with  argentic  oxide 
or  carbonate,  and  evaporating  the  clear  solution  to  perfect 
dryness.  It  is  extremely  soluble  in  water  and  easily  fusible. 
The  electrical  relations  of  substances  in  the  fused  salt  I  found 
to  be  as  follows,  the  first-named  substance  being  the  most 
positive — silver,  platinum,  charcoal  of  lignum-vitae,  palladium, 
gold ;  and  in  a  dilute  aqueous  solution  of  the  salt — aluminium, 
magnesium,  silicon,  indium,  rhodium,  and  carbon  of  lignum- 
vitse,  platinum,  silver,  palladium,  tellurium,  gold  (*  Chemical 
News,'  vol.  xxi  p.  28). 

L  2 


1 48  The  A  rt  of  Electro-Metallurgy. 

Nearly  all  the  salts  of  silver  (except  the  sulphide)  become 
converted  into  the  cyanide  by  immersion  in  a  solution  of 
cyanide  of  potassium,  and  therefore  the  nitrate  and  chloride 
are  sometimes  used  instead  of  the  cyanide,  to  form  with 
.cyanide  of  potassium  the  plating  liquid.  But  this  is  a 
bad  mode  of  procedure,  because  the  same  amount  of 
materials  is  used,  and  nitrate  or  chloride  of  potassium  are 
thereby  introduced  into  the  plating  liquid,  and  these  sub- 
stances are  objectionable. 

Cyanide  of  silver  is  generally  prepared  by  adding  a  solu- 
tion of  cyanide  of  potassium  to  one  of  nitrate  of  silver  just  as 
long  as  a  precipitate  occurs  ;  the  white  precipitate,  which  is 
cyanide  of  silver,  is  insoluble  in  water,  and  is  not  perceptibly 
soluble  in  commercial  hydrocyanic  acid  ;  it  dissolves  very 
freely  in  a  solution  of  cyanide  of  ammonium,  potassium,  or 
sodium,  and  in  hyposulphite  of  soda  solution  ;  it  is  also 
soluble  in  solutions  of  ammonia,  carbonate  of  ammonia, 
sal-ammoniac,  nitrate  of  ammonia,  and  ferro-cyanide  of  po- 
tassium. 

Chemical  characters  of  cyanide  of  silver.  —According  to 
Messrs.  Glassford  and  Napier,  cyanogen  in  the  presence  of 
cyanide  of  potassium,  possesses  a  greater  affinity  than  any 
other  substance  for  silver;  decomposing  every  salt  of  that 
metal  except  the  sulphide,  and  forming  cyanide  of  silver. 

In  dissolving  the  oxide,  carbonate,  chloride,  or  ferro- 
cyanide  of  silver,  in  a  solution  of  cyanide  of  potassium, 
they  are  all  decomposed,  and  cyanide  of  silver  is  always 
formed.  Cyanide  of  silver  should  be  dried  below  260°  Fahr. 
Hydrochloric  acid  decomposes  it  with  evolution  of  hydro- 
cyanic acid  gas ;  cold  nitric  acid  has  no  action  upon  it ;  a 
boiling  mixture  of  sulphuric  acid  and  water  decomposes  it, 
with  escape  of  hydrocyanic  acid  gas,  and  formation  of  sul- 
phate of  silver ;  it  is  soluble  in  solutions  of  the  alkaline 
chlorides,  but  its  best  solvent  is  an  aqueous  solution  of  cyanide 
of  potassium,  of  which  salt  it  requires  one  equivalent  (sixty- 
five  parts),  to  dissolve  one  equivalent  (134  parts).  The 


Electrolysis  of  Salts  of  Silver.  149 

resulting  solution,  when  evaporated,  yields  crystals  of  double 
cyanide  of  silver  and  potassium,  which  are  soluble  in  eight 
parts  of  cold  and  in  one  part  of  boiling  water.  The  solution 
of  this  double  salt,  which  is  nearly  the  same  as  the  ordinary 
plating  solution,  may  be  boiled  for  any  length  of  time  without 
being  decomposed,  and  it  is  very  little  affected  by  light  \  it  is 
decomposed  by  all  acids,  and  they  precipitate  the  silver  as 
cyanide  of  silver ;  the  hydro-acids — hydrochloric  acid  for  ex- 
ample— decompose  the  cyanide  of  silver  also  ;  sulphuretted 
hydrogen  precipitates  the  silver  as  sulphide  of  silver  (*  Philo- 
sophical Magazine,'  vol.  xxv.,  1844,  pp.  56-71).  According  to 
Baup,  the  double  cyanide  of  silver  and  potassium  (K  Cy, 
Ag  Cy)  requires  for  solution  four  parts  of  water,  or  twenty-five 
parts  of  85  per  cent,  alcohol,  each  at  20°  C.  It  does  not 
become  discoloured  by  exposure  to  sunshine,  nor  make 
stains  upon  paper  nor  on  the  skin.  The  double  cyanide 
of  silver  and  sodium  (Na  Cy,  Ag  Cy)  dissolves  in  five  parts 
of  water,  or  twenty-four  parts  of  85  per  cent,  alcohol,  at 
20°  C. 

Electrolysis  of  salts  of  silver. — A  highly- concentrated  so- 
lution of  argentic  nitrate,  made  as  neutral  as  possible,  is 
easily  decomposed,  and  yields  coherent  metal  by  a  sufficiently 
feeble  current.  An  anode  of  silver  is,  however,  indispen- 
sable (Becquerel,'  Chemical  News,'  vol.  vi.  p.  126).  I  have 
electrolysed  a  solution  of  argentic  nitrate,  and  obtained  a 
thick,  black,  insoluble  crust  upon  the  silver  anode  ;  the 
crust  was  probably  a  peroxide  of  silver,  but  it  also  contained 
a  compound  of  nitrogen.  Fused  argentic  nitrate  yields  silver 
at  the  cathode  and  oxygen  gas  at  the  anode.  Fused  chloride 
of  silver  is  resolved  into  silver  and  chlorine. 

The  sulphate  of  silver  is  too  sparingly  soluble,  and  too 
bad  a  conductor  to  be  of  much  value  in  electro-plating. 
The  hyposulphite  is  much  more  soluble,  and  has  been  used 
for  practical  purposes,  but  abandoned.  Solutions  of  nitrate, 
chloride,  and  carbonate  of  silver  in  excess  of  aqueous  am- 
monia have  also  been  tried.  They  are  good  conductors,  but 


150  The  A  rt  of  Electro-Metallurgy. 

contain  argentate  of  ammonia  or  fulminate  of  silver,  which 
is  an  extremely  dangerous  substance  when  in  a  dry  state, 
and  detonates  with  fearful  violence  by  the  slightest  friction 
or  percussion.  The  iodide  of  silver  and  potassium,  the 
acetate  of  silver,  the  sulphocyanide  of  silver  and  potassium, 
and  the  potassio-tartrate  of  silver,  have  all  been  tried  for 
depositing  purposes,  but  do  not  appear  to  equal  the  double 
cyanide  of  silver  and  potassium  ;  in  the  electrolysis  of  all 
of  them  there  is  occasionally  observed  a  black  crust,  pro- 
bably containing  some  peroxide  of  silver,  upon  the  silver 
anode. 

I  have  electrolysed  artificially-chilled  anhydrous  hydro- 
fluoric acid  by  means  of  a  pure  silver  anode,  and  a  current 
from  ten  Smee's  cells.  The  current  was  conducted  more 
freely  than  with  an  anode  of  palladium,  and  still  more  so 
than  with  one  of  gold ;  the  anode  corroded  rapidly,  and  be- 
came covered  first  with  some  black  powder  upon  its  edges, 
and  then  with  a  grey  powder  (probably  metallic  silver)  which 
contained  only  a  trace  of  soluble  silver  salt.  I  also  electro- 
lysed a  saturated  neutral  aqueous  solution  of  argentic  fluoride 
with  a  current  from  six  Grove's  cells,  a  small  platinum  anode 
and  a  large  platinum  cathode.  Free  conduction  occurred, 
no  gas  or  odour  was  evolved,  a  thick,  hard,  and  strongly  ad- 
herent, black  crust  quickly  formed  upon  the  anode,  and  a 
rapid  deposit  of  yellowish  scales  of  silver  upon  the  cathode  ; 
the  crystals  soon  extended  upwards  and  united  the  elec- 
trodes. From  the  behaviour  of  the  black  crust  with  strong 
nitric,  hydrochloric,  and  sulphuric  acids,  and  also  with 
aqueous  ammonia  ;  and  from  its  evolving,  when  heated  to 
redness,  a  gas  which  re-inflamed  a  red-hot  splint  explosively, 
and  losing  nearly  the  theoretical  proportion  by  weight  in  the 
process,  and  leaving  metallic  silver,  I  concluded  the  crust 
to  be  peroxide  of  silver  (Ag2  O2).  By  the  electrolysis  of  a 
more  dilute  solution  a  similar  crust  was  formed,  but  gas  was 
also  evolved  at  the  anode. 

I  also  made  a  number  of  experiments  of  electrolysing 


Deposition  of  Silver  by  Simple  Immersion.      1 5  r 

argentic  fluoride  in  a  fused  state  with  platinum  electrodes, 
in  a  covered  platinum  cup,  with  a  current  from  six  Smee's 
elements.  In  each  case  conduction  commenced  before  the 
salt  had  fused  ;  and  when  the  salt  was  liquid  the  conduc- 
tion was  as  perfect  as  if  the  electrodes  were  united  by  a 
metal  wire.  No  signs  of  genuine  electrolysis  could  be  de- 
tected in  either  instance.  I  also  electrolysed  the  fused  salt 
with  a  rod  of  highly-ignited  charcoal  of  lignum- vitae,  and  a 
current  from  ten  Smee's  cells,  but  only  a  small  amount  of 
conduction  occurred  in  consequence  of  the  resistance  of  the 
carbon.  The  anode  was  corroded  and  evolved  gas  (See 
*  Phil.  Trans.  Royal  Society,'  1870,  p.  234;  '  Chemical  News/ 
vol.  xxi.  p.  28). 

According  to  F.  Wohler,  if  a  current  from  two  Bunsen's 
cells  is  passed  through  a  dilute  solution  of  sulphuric  acid  or 
sodic  sulphate  by  means  of  a  silver  anode,  the  anode  be- 
comes covered  with  black  amorphous  argentic  peroxide,  and 
this  oxidation  is  due  to  ozone.  With  a  solution  of  potassic 
nitrate  similarly  treated,  flocculent  light-brown  argentic  oxide 
is  formed.  In  one  of  potassic  ferro- cyanide,  the  anode  ac- 
quires a  film  of  white  amorphous  argentic  ferro-cyanide.  And 
in  a  solution  of  potassic  dichromate  it  becomes  covered 
with  a  reddish  black  film  of  crystallised  argentic  chromate 
('Chemical  News/  vol.  xviii.  p.  189). 

The  electrolysis  of  melted  caustic  soda  with  an  anode  of 
silver  causes  the  silver  to  dissolve  and  be  deposited  upon 
the  platinum  cathode ;  but,  on  cleaning  the  cathode  with 
nitric  acid,  a  black  powder  of  platinum  is  left  (Brester, 
'  Chemical  News/  vol.  xviii.  p.  145).  I  have  repeatedly  met 
with  a  similar  effect  with  fluoride  of  silver  melted  in  vessels 
of  platinum. 

Deposition  of  silver  by  simple  immersion  (see  pp.  77,  78). 
— Aluminium  throws  down  the  silver  irom  acid  or  neutral 
solutions  of  argentic  nitrate ;  slowly  in  dilute  solutions  ;  also 
immediately  from  solutions  of  chloride  or  chromate  of  silver 
in  aqueous  ammonia.  It  rapidly  decomposes  chloride  of 


152  The  Art  of  Electro-Metallurgy. 

silver  in  a  state  of  fusion,  evolving  great  heat  (A.  Cossa, 
Watts'  '  Dictionary  of  Chemistry,'  2nd  Supplement,  p.  54). 

A  solution  of  sulphate  of  silver  is  not  reduced,  but  one 
of  argentic  nitrate  deposits  its  silver  by  contact  with  hydrogen, 
obtained  by  a  variety  of  methods  (Brester,  '  Chemical  News,' 
vol.  xviii.  p.  144).  According  to  J.  Spiller,  electro  deposited 
nickel  does  not  deposit  silver  from  a  solution  of  argentic 
nitrate  ('Chemical  News,'  vol.  xxiv.  p.  175). 

I  have  observed  that  hydrogen  deposits  silver  from  semi- 
fused  argentic  fluoride  ('  Chemical  News,'  vol.  xxi.  p.  28) ; 
also  that  carbon  and  crystalline  boron  do  not  separate  silver 
from  that  salt  at  a  red  heat,  nor  does  boron  separate  it  from  an 
aqueous  solution  of  that  salt ;  that  crystals  of  silicon  thrown 
upon  melted  argentic  fluoride  become  red-hot,  undergo  rapid 
combustion,  forming  fluoride  of  silicon  and  depositing  silver  ; 
that  those  crystals  also  deposit  crystals  of  silver  slowly  from  an 
aqueous  solution  of  that  salt ;  and  from  a  mixture  of  solution 
of  argentic  fluoride,  hydrofluoric  acid,  and  nitric  acid,  they 
liberate  bubbles  of  spontaneously  inflammable  siliciuretted 
hydrogen  gas  ('Chemical  News,'  vol.  xxiv.  p.  291).  A  frag- 
ment of  stannous  fluoride  also  deposited  metallic  silver  from 
an  aqueous  solution  of  argentic  fluoride  in  a  platinum  dish. 

According  to  Raoult,  gold  in  contact  with  silver  in  a  cold 
or  hot  acid  or  neutral  solution  of  a  salt  of  silver  receives  no 
deposit  of  that  metal  (;  Journal  of  Chemical  Society/  vol.  ii. 
p.  465). 

Silvering  by  simple  immersion. — This  process  is  chiefly 
applicable  to  small  articles,  such  as  pins,  buttons,  buckles, 
coffin  nails,  hooks  and  eyes,  &c.  where  only  a  very  thin  coat- 
ing of  silver  is  required.  The  following  solutions,  in  the 
proportions  indicated,  are  used  by  adding  a  small  quantity 
of  water  sufficient  to  form  the  ingredients  into  a  pasty  liquid 
of  the  consistence  of  cream,  stirring  the  articles  thoroughly 
about  in  it,  or  rubbing  them  over  with  it,  until  they  have  ac- 
quired the  desired  degree  of  whiteness. 

i st.  Take  equal  parts  of  chloride  of  silver  and  bitartrate 


Silvering  by  Simple  Immersion.  153 

of  potash.  2nd.  Take  chloride  of  silver  one  part,  alum  two 
parts,  common  salt  eight  parts,  and  cream  of  tartar  eight 
parts.  3rd.  Take  chloride  of  silver  one  part,  prepared  chalk 
one  part,  common  salt  one  and  a  quarter  part,  and  pearlash 
three  parts.  4th.  A  '  novargent '  solution  for  resilvering  old 
plated  goods  consists  of  100  parts  of  hyposulphite  of  soda, 
and  chloride  or  any  other  salt  of  silver,  fifteen  parts.  Com- 
pounds of  this  description  are  also  used  for  silvering 
clock  faces,  thermometer  and  barometer  plates,  and  many 
other  articles  of  copper  and  brass.  Or  one  part  of  chloride 
of  silver  mixed  with  eighty  or  100  parts  of  cream  of  tartar  (bi- 
tartrate  of  potassium),  to  which  may  be  added  or  not  about 
eighty  or  100  parts  of  common  salt,  is  dissolved  in  boiling 
water,  and  the  articles  contained  in  a  basket  are  immersed, 
and  stirred  about  in  the  hot  liquid.  An  old  solution  is  of  a 
green  colour  from  the  presence  of  dissolved  copper,  and 
works  better  than  a  new  one.  If  there  is  the  least  particle 
of  metallic  zinc  or  iron  present,  it  causes  a  red  deposit  of 
copper  upon  the  articles.  Another  solution  employed  for  a 
similar  purpose  is  composed  of  1000  parts  of  water,  sixty 
parts  of  cyanide  of  porassium,  and  ten  parts  of  nitrate  of 
silver ;  it  is  used  at  a  boiling  temperature.  The  action  of 
this  bath  depends  upon  the  fact  that  copper  is  more  electro- 
positive to  silver  in  proportion  to  the  excess  of  free  cyanide  of 
potassium  present 

The  following  solution  of  the  double  sulphite  of  silver 
and  sodium,  according  to  Roseleur,  may  be  used  cold.  It 
is  prepared  as  follows  :  Dissolve  four  parts  of  crystals  of 
washing  soda  in  five  parts  of  distilled  water.  Pass  sul- 
phurous anhydride  gas  (SO2)  through  the  liquid  by  bub- 
bling it  through  mercury  at  the  bottom  of  the  vessel  to  pre- 
vent the  exit  tube  becoming  clogged  with  crystals,  until  the 
liquid  redissolves  the  crystals  of  bicarbonate  and  slightly 
reddens  blue  litmus  paper.  Set  it  aside  for  twenty -four  hours 
to  allow  some  bisulphite  of  sodium  to  crystallise  out.  Take 
the  liquid  part  only,  stir  it  well  to  remove  carbonic  acid. 


154  The  A  rt  of  Electro-Metallurgy. 

Now  add,  if  it  is  alkaline,  some  more  sulphurous  gas,  or  if  it 
is  acid,  a  little  more  carbonate,  until  the  liquid  after  stirring 
renders  blue  litmus  paper  violet  or  slightly  red.  To  the 
clear  liquid  add,  with  stirring,  a  solution  of  argentic  nitrate, 
until  the  precipitate  produced  begins  to  be  slow  in  dissolv- 
ing ;  the  solution  is  then  ready. 

This  liquid  is  said  to  be  '  always  ready  to  work,  and  pro- 
duces quite  instantaneously  a  magnificent  silvering  upon 
copper,  bronze,  or  brass  articles,  which  have  been  thoroughly 
cleansed,  and  passed  through  a  weak  solution  of  nitrate  of 
binoxide  of  mercury,  although  this  last  operation  is  not  ab- 
solutely necessary.'  The  bath  is  renewed  by  addition  of 
nitrate  of  silver,  and  sooner  or  later  also  some  bisulphite  of 
soda.  Some  of  the  silver  of  the  solution  deposits  itself  upon 
the  sides  of  the  vessel.  Roseleur  states  that  he  has  used 
this  bath  for  five  consecutive  years,  and  has  daily  silvered  in 
it  '  as  many  articles  as  a  man  could  conveniently  carry,  and 
at  prices  varying  ten  cents  to  two  dollars  per  kilogramme,' 
and  he  '  does  not  doubt  that  it  would  eventually  replace  all 
the  other  known  methods.  He  further  states  that  the  deposit, 
without  the  aid  of  electricity,  may  become  nearly  as  thick  as 
desired,  and  in  direct  ratio  to  the  length  of  the  immersion.' 

This  particular  process  differs  from  nearly  all  other  ones 
of  metallic  deposition  upon  metals,  in  being  only  in  part  an 
electrical  action.  When  a  metallic  article  is  immersed  in 
a  bath  of  another  metal,  in  which  it  coats  itself,  a  portion  of 
the  immersed  metal  dissolves  and  generates  an  electric  cur- 
rent, which  decomposes  the  liquid,  and  deposits  an  equiva- 
lent of  the  other  metal  as  a  coating  upon  the  immersed 
article ;  this  deposited  film  arrests  the  action,  and  prevents 
a  thick  coating  being  formed.  But  in  this  particular  liquid 
a  spontaneous  chemical  change  also  takes  place  ;  the  sul- 
phurous anhydride  of  the  sulphite  of  silver  takes  oxygen  to 
itself,  to  form  sulphuric  anhydride,  and  sets  the  silver  free, 
and  this  silver  adheres  to  the  articles,  and  to  the  vessel  con- 
taining the  liquid.  The  sulphuric  anhydride  unites  with 


Solutions  for  Plating  by  a  Separate  Current.     155 

some  of  the  soda  of  the  undecomposed  portion  of  the  sul- 
phite and  liberates  sulphurous  anhydride,  and  forms  sulphate 
and  bisulphite  of  sodium.  The  process  is  partly  like  that  of 
coating  looking-glasses  with  pure  silver. 

Silvering  by  contact  with  zinc  (see  p.  82). — Mr.  Joseph 
Steele  took  out  a  patent,  dated  August  Qth,  1850,  for  silvering 
articles  by  immersing  them  in  a  silver  solution  in  contact 
with  a  piece  of  zinc  of  proper  size.  The  process  is  as 
follows  :  Dissolve  four  ounces  of  pure  silver  in  twenty  ounces 
of  nitric  acid  ;  also  dissolve  separately  one  and  a  half  pound 
of  common  salt  in  one  and  a  half  gallon  of  water ;  mix  the  two 
solutions  together ;  allow  the  mixture  to  remain  until  clear, 
pour  away  the  clear  liquid,  and  wash  the  precipitate,  which 
is  chloride  of  silver ;  next  fuse  together  twenty- four  ounces 
of  ferro-cyanide  of  potassium  and  twelve  ounces  of  carbonate 
of  potash,  and,  when  the  mass  is  cold,  add  it,  together  with 
the  chloride  of  silver,  to  one  gallon  .and  a  half  of  water,  boil 
the  mixture  and  filter  it ;  it  is  then  ready  for  use. 

Solutions  for  plating  by  separate  current  (see  p.  86). — 
These  may  be  made  either  by  chemical  means  or  by  the  aid 
of  an  electric  current.  The  best  solution  for  general  purposes 
is  the  double  cyanide  of  silver  and  potassium,  and  when  re- 
quired in  large  quantities  it  is  usually  made  by  chemical 
means.  Many  solutions  have  been  proposed  and  tried  for 
depositing  silver  by  the  battery  process,  but  none  have  stood 
the  test  of  time  and  experience  like  the  one  composed  of 
double  cyanide  of  silver  and  potassium  dissolved  in  water, 
and  a  little  free  cyanide  of  potassium  added.  It  must,  how- 
ever, always  be  remembered,  when  making  cyanide  deposit- 
ing solutions  with  the  aid  of  potassic  cyanide,  that  the  com- 
position of  this  salt  as  usually  sold  is  extremely  variable,  and 
unless  the  depositor  is  aware  of  this  he  may  be  led  quite 
astray  in  his  calculations,  and  unwittingly  introduce  various 
impurities  into  his  depositing  liquids. 

Ordinary  cyanide  plating  solution  may  be  made  of 
various  strengths,  from  half  an  ounce  of  silver  to  the  gallon 


1 56  The  A  rt  of  Electro- Metallurgy. 

of  water,  to  two,  four,  six,  or  more  ounces,  and  from  an 
ounce  of  cyanide  of  potassium  to  several  pounds  per  gallon, 
and  still  be  effective  in  working.  One  part  of  silver  in  zoo 
parts  of  solution  is  enough  for  ordinary  purposes,  but  a  good 
proportion  is  two  or  two  and  a  half  in  TOO  ;  some  platers  use 
as  much  as  ten  in  100.  The  following  proportions  were 
employed  by  M.  Roulz,  viz.  a  solution  of  one  part  by  weight 
of  cyanide  of  silver  and  ten  parts  of  cyanide  of  potassium,  in 
100  parts  of  water;  the  mixture  being  diluted  with  water  to 
the  desired  strength. 

Making  cyanide  of  silver  plating  solution  by  chemical  means. 
—Take  four  parts  of  grain  silver,  add  it,  in  small  portions  at 
a  time,  to  a  warm  mixture  of  about  six  and  a  half  parts  by 
weight  of  pure  and  strong  nitric  acid,  and  one  part  of  water, 
contained  in  a  capacious  glass  or  stoneware  vessel.  Gas  will 
be  evolved  from  the  surfaces  of  the  pieces  of  silver,  and 
reddish-brown  fumes  of  nitrous  anhydride  will  arise  from  the 
mixture,  and  should  be  conveyed  out  of  the  apartment  by 
means  of  a  chimney.  The  action  should  be  maintained 
moderate  and  uniform,  and,  if  it  should  become  too  strong,  a 
little  cold  distilled  water  should  be  added,  and  the  mixture 
kept  more  cool ;  when  the  whole  of  the  metal  is  dissolved, 
evaporate  the  solution  nearly  to  dryness,  which  will  drive  off 
any  excess  of  acid  that  may  be  present ;  the  resulting  salt, 
nitrate  of  silver,  may  then  be  dissolved  in  a  large  quantity 
of  distilled  water,  in  the  proportion  of  half  a  gallon  (more  or 
less)  to  each  ounce  of  the  silver  used.  At  the  same  time  a 
solution  should  be  made  of  from  two  to  three  parts  (accord- 
ing to  its  quality)  of  cyanide  of  potassium  in  twenty  or  thirty 
parts  of  distilled  water,  which  is  to  be  added  gradually  to  the 
solution  of  nitrate  of  silver  as  long  as  it  produces  a  precipi- 
tate ;  if  too  much  be  added,  it  will  cause  some  of  the  pre- 
cipitate to  redissolve  and  be  wasted  ;  it  will  also  make  the 
liquid  appear  clear  and  slightly  brown  where  it  passes  ;  in 
such  a  case  the  liquid  should  be  stirred,  then  allowed  to  settle 
clear,  and  a  small  quantity  of  nitrate  of  silver  dissolved  in 


Making  Silver  Plating  Solutions.  157 

distilled  water  should  be  added  as  long  as  it  produces  a  white 
cloud.  By  conducting  the  operation  in  a  glass  vessel,  add- 
ing the  liquid  towards  the  latter  period  in  small  quantities 
at  a  time,  and  at  intervals  of  a  few  minutes  each,  with  gentle 
stirring  immediately  upon  each  addition,  carefully  observing 
when  it  ceases  to  produce  a  precipitate,  the  point  of  neutral- 
isation may  be  very  accurately  arrived  at.  The  liquid  must 
now  be  allowed  to  remain  undisturbed  until  quite  clear,  the 
clear  portion  poured  steadily  away  from  the  precipitate  of 
cyanide  of  silver,  and  the  precipitate  washed  five  or  six  times 
in  a  large  quantity  of  water,  by  simply  adding  the  water 
briskly  to  it,  allowing  it  to  settle,  and  then  pouring  away  the 
clear  portion.  Next  dissolve  from  six  to  eight  parts  (accord- 
ing to  its  quality)  of  cyanide  of  potassium  in  twenty  parts  of 
distilled  water,  adding  it  in  portions  at  a  time  to  the  wet 
cyanide  of  silver,  with  free  stirring,  until  barely  the  whole  is 
dissolved ;  then  add  about  three  parts  more  of  cyanide  of 
potassium  to  form  free  cyanide,  and  sufficient  distilled  water 
to  reduce  the  whole  to  the  proportion  of  about  one  ounce 
of  silver  to  the  gallon  ;  finally,  when  all  the  free  cyanide  is 
dissolved,  filter  the  solution  through  a  piece  of  unglazed 
calico.  On  the  small  scale,  distilled  water  is  used  in  all 
the  various  parts  of  the  process,  except  the  washing ;  but, 
on  the  large  scale,  clean  rain-water  may  be  used  in  all  the 
operations. 

If  either  the  nitric  acid,  or  the  water  in  which  the  nitrate 
of  silver  is  dissolved,  contains  chlorides,  a  white  residue  of 
chloride  of  silver  will  be  left  on  dissolving  the  nitrate  ;  and 
if  a  small  amount  of  brown  matter  is  left  on  dissolving  the 
cyanide  of  silver  in  the  cyanide  of  potassium  solution,  it 
arises  from  decomposition  of  some  of  the  latter  salt.  The 
insoluble  matters  and  the  wash- waters  should  be  reserved 
for  the  purpose  of  recovering  from  them  any  traces  of  silver 
they  may  contain.  The  numbers  given  above  are  based  upon 
the  assumption  that  the  cyanide  of  potassium  employed  is 
of  an  average  quality,  and  contains  about  50  per  cent,  of  the 


1 5  8  The  A  rt  of  Electro-Metallurgy. 

actual  substance ;  in  proportion  as  the  percentage  is  higher, 
so  will  the  quantity  required  be  less. 

The  following  solution  is  said  to  be  an  excellent  one ; 
water  1000  parts,  pure  cyanide  of  potassium  fifty  parts,  silver, 
for  converting  into  cyanide,  twenty-five  parts.  The  silver  is 
converted  into  nitrate.  The  nitrate  is  dissolved  in  distilled 
water,  and  prussic  acid  added  until  it  produces  no  more 
precipitate.  The  cyanide  of  silver  is  filtered  and  washed, 
and  then  added  to  the  water  and  cyanide  of  potassium. 
This  method  is  only  suitable  for  making  small  quantities  of 
solution,  because  the  ordinary  prussic  acid  is  so  dilute. 

Some  operators  have  employed  the  plan  of  forming 
cyanide  of  silver  by  generating  hydrocyanic  acid  gas,  by 
heating  a  mixture  of  dilute  sulphuric  acid  and  coarsely- 
powdered  ferro-cyanide  of  potassium  in  a -glass  flask,  and 
passing  the  evolved  hydrocyanic  acid  (prussic  acid)  vapour 
through  a  solution  of  argentic  nitrate  as  long  as  a  precipitate 
is  formed,  and  this  yields  a  slightly  purer  cyanide  of  silver 
than  that  prepared  by  precipitation,  but  it  is  a  slow  and  not 
an  economical  process,  and  the  prussic  acid  vapour  is  highly 
dangerous  to  inhale. 

The  cyanide  of  silver  plating  solution  may  be  made  by 
other  modifications  of  the  chemical  method  than  the  one 
described  ;  for  instance,  some  depositors  make  the  solutions 
by  adding  oxide,  carbonate,  or  even  chloride  of  silver  to  a 
solution  of  cyanide  of  potassium,  as  long  as  it  will  dissolve, 
and  then  adding  an  amount  of  free  cyanide  ;  by  this  process 
the  depositor  is  enabled  to  use  caustic  potash,  carbonate 
of  potash,  hydrochloric  acid,  or  common  salt,  instead  of 
cyanide  of  potassium,  for  precipitating  the  nitrate  of  silver ; 
nevertheless  it  still  requires  two  equivalents  of  cyanide  of 
potassium  to  be  used  as  before,  viz.  one  to  convert  the  salt 
of  silver  into  cyanide,  and  the  other  to  dissolve  the  cyanide 
of  silver  formed,  because,  in  all  such  cases,  according  to  the 
researches  of  Messrs.  Glassford  &  Napier  ('  Philosophical 
Magazine,'  1844),  when  any  salt  of  silver  is  added  to  a  solu- 


Making  Silver  Plating  Solutions.  159 

tion  of  cyanide  of  potassium,  it  is  first  converted  into  cyanide 
of  silver  at  the  expense  of  one  portion  of  the  cyanide  of  po- 
tassium, it  then  combines  with  the  remaining  cyanide  to 
form  double  cyanide  of  silver  and  potassium,  which  dissolves 
in  the  water,  therefore  by  this  modification  of  the  chemical 
method  no  cyanide  of  potassium  is  saved,  and  the  carbon- 
ate of  potash,  hydrochloric  acid,  &c.,  are  wasted.  This 
modification  has  a  still  greater  disadvantage  ;  it  introduces 
substances  into  the  depositing  liquid  which  are  injurious. 
A  good  depositing  solution  should  dissolve  the  anode  freely, 
hold  abundance  of  metal  in  solution,  and  not  act  chemically 
upon  base  metals,  because  it  is  such  metals  we  generally 
wish  to  coat ;  now,  if  instead  of  cyanide  of  silver  we  add 
oxide  of  silver  to  the  cyanide  of  potassium  liquid,  it  converts 
part  of  the  cyanide  into  caustic  potash  ;  if  we  add  carbonate 
of  silver,  it  converts  it  into  carbonate  of  potash ;  and  if 
chloride  of  silver,  it  converts  it  into,  chloride  of  potassium  ; 
and  each  of  these  substances,  especially  the  last,  diminishes 
the  action  of  the  liquid  upon  the  dissolving  plate,  decreases 
its  solvent  power  for  cyanide  of  silver,  makes  its  particles 
less  mobile,  and  causes  it  to  act  in  some  degree  upon  base 
metals,  and  thus  endangers  the  adhesion  of  the  deposits 
upon  them.  Some  electro-platers  think  the  presence  of 
these  salts  not  injurious,  but  most  consider  them  highly 
detrimental.  One  hundred  ounces  of  silver,  converted  into 
chloride,  and  dissolved  in  cyanide  of  potassium  solution, 
produces  s:xty-nine  ounces  of  chloride  of  potassium  as  an 
impurity  in  the  liquid  ;  or  if  converted  into  nitrate,  and  so 
dissolved,  produces  ninety-three  and  a  half  ounces  of  nitrate 
of  potassium  as  impurity. 

A  good  plating  liquid  should  contain  one  equivalent 
(sixty-five  parts)  of  pure  cyanide  of  potassium,  and  one 
equivalent  (134  parts)  of  cyanide  of  silver,  besides  about  20  to 
50  per  cent,  of  free  cyanide,  and  sufficient  water  to  form  a 
thin  liquid.  It  is  necessary  to  have  free  cyanide,  because  in 
working  the  solution  insoluble  cyanide  of  silver  is  formed  at 


1 60  The  A  rt  of  Electro-Metallurgy. 

the  anode,  and  requires  free  cyanide  of  potassium  to  com- 
bine with  it  and  form  the  soluble  double  cyanide ;  at  the 
same  time  cyanogen  and  cyanide  of  potassium  are  set  free 
at  the  cathode,  or  receiving  surface,  by  the  deposition  of  the 
silver  ;  and  as  it  requires  some  time  for  those  substances  to 
mix  with  the  liquid,  and  reach  the  dissolving  plate,  sufficient 
free  cyanide  must  be  provided  ;  the  necessity  of  having 
sufficient  water  to  form  a  thin  liquid  arises  from  the  double 
cyanide  formed  at  the  dissolving  plate  being  specifically 
heavier  than  the  solution,  and  thus  having  a  tendency  to 
sink  to  the  bottom,  whilst  the  hydrocyanic  acid  and  cyanide 
of  potassium,  set  free  at  the  surface  of  the  articles,  being 
specifically  lighter,  tend  to  rise  to  the  surface  ;  at  the  same 
time  each  of  them  mixes  more  or  less  with  the  surrounding 
liquid  by  capillary  attraction  or  adhesion,  and  the  more 
dilute  the  liquid  is,  the  more  mobile  are  its  particles,  and 
the  more  rapidly  does  this  mixture  take  place.  This 
explains  why  strong  silver  solutions  require  more  frequent 
stirring  than  weak  ones  to  keep  them  uniform.  In  some 
manufactories,  where  they  have  steam  power  at  command, 
the  articles  are  kept  in  constant  motion  by  machinery 
swinging  them  gently  to  and  fro,  but  in  small  electro-plating 
establishments  the  silver  solutions  are  stirred  every  evening 
instead. 

Many  electro-platers  use  a  cyanide  solution  containing 
about  half  an  ounce  of  silver  to  the  gallon,  and  add  a  very 
large  proportion  of  free  cyanide  to  make  it  conduct  freely  ; 
such  a  solution  has  the  advantage  of  being  comparatively 
inexpensive  in  its  first  formation,  quick  in  working,  and 
yields  metal  of  an  average  character  ;  but  it  is  rather 
difficult  to  manage  in  hot  weather,  and  dissolves  the  anode 
very  rapidly,  on  account  of  the  large  proportion  of  free 
cyanide.  In  practice,  the  amount  of  silver  to  the  gallon 
varies  from  half  an  ounce  to  about  four  ounces,  but  ordinary 
solutions  contain  about  one  or  two  ounces  to  the  gallon ; 
the  amount  of  free  cyanide  of  potassium  also  varies  from 


Silver  Electro-Plating  Solutions.  161 

about  half  the  weight  of  the  silver  dissolved  in  the  liquid,  to 
five  or  ten  times  this  quantity.  A  very  good  proportion,  is 
about  three-fourths  of  the  weight  of  the  dissolved  silver, 
but  there  is  no  rule  generally  recognised  in  the  trade  upon 
this  point ;  some  manufacturers  use  a  very  large,  and  others 
a  very  small  proportion. 

Mr.  Alexander  Parkes  took  out  a  patent,  dated  March 
29th,  1871,  for  improvements  in  the  solid  deposition 
of  silver.  He  converts  an  ounce  of  silver  into  oxide, 
by  first  dissolving  it  in  nitric  acid,  and  then  precipitating  it 
by  caustic  potash ;  he  then  dissolves  the  oxide,  together 
with  sixteen  ounces  of  cyanide  of  potassium,  in  two  gallons  of 
water,  and  uses  the  resulting  liquid  for  depositing  solid  articles. 

Solid  articles  of  silver  are  occasionally  made,  by  first 
forming  a  thin  mould  in  copper  by  the  electrotype  process, 
and  then  depositing  silver  upon  this  mould  in  a  cyanide 
solution  (containing  about  eight  ounces  of  silver  per  gallon), 
until  the  deposit  is  sufficiently  thick.  The  article  is  then 
immersed  in  a  boiling  solution  of  dilute  hydrochloric  acid, 
or  in  a  hot  one  of  perchloride  of  iron,  until  all  the  copper 
is  dissolved. 

Mr.  Edmund  Tuck  took  out  a  patent,  June  4,  1842,  for 
'  improvements  in  depositing  silver  upon  german-silver.' 
For  plating  the  commoner  quality  of  that  alloy,  he  uses  a 
liquid  composed  of  sulphate  of  silver,  dissolved  in  a  solution 
of  carbonate  of  ammonium,  and  for  the  best  quality,  he 
uses  cyanide  of  silver  dissolved  in  a  similar  liquid.  The 
mixtures  are  formed,  by  dissolving  seventy  parts  of  the 
carbonate  in  distilled  water,  then  adding  156  parts  of  sul- 
phate of  silver,  or  134  of  cyanide  of  silver,  and  boiling 
the  liquid  until  the  silver  salt  is  dissolved.  For  coating 
common  german-silver,  he  adds  half  an  ounce  of  sulphate 
of  silver,  to  a  solution  of  107  grains  of  bicarbonate  of 
ammonium. 

One  plater  recommends  the  use  of  two  liquids,  the  first 
to  '  whiten,'  and  the  second  to  *  finish.7  The  whitening 

M 


1 62  The  A  rt  of  Electro-Metallurgy. 

one  is  composed  of  one  gallon  of  distilled  water,  two 
and  a  half  troy  pounds  of  cyanide  of  potassium,  eight 
ounces  of  carbonate  of  soda,  and  five  of  cyanide  of  silver ; 
and  the  finishing  solution,  of  one  gallon  of  distilled 
water,  four  and  a  half  troy  ounces  of  cyanide  of  potassium, 
and  one  and  a  half  of  cyanide  of  silver;  using  a  series 
of  from  three  to  ten  Smee's  cells  with  the  first  solution,  and 
one  large  cell  only  foi  the  second,  and  keeping  the  anode 
and  articles  in  the  second  solution,  as  closely  together  as 
possible.  By  these  means,  the  silver  may  be  made  to  adhere 
firmly  to  all  kinds  of  brass,  bronze,  type-metal,  &c.,  with- 
out the  use  of  mercury. 

Copper,  brass,  and  german- silver,  are  the  best  substances 
to  deposit  silver  upon  ;  lead  is  a  very  bad  metal  for  the  pur- 
pose, because  it  is  so  soft.  Articles  formed  of  zinc,  or  iron, 
are  usually  coated  with  a  film  of  copper,  in  a  cyanide  solution, 
before  putting  them  into  the  plating  liquid.  Those  formed 
of  Britannia-metal,  tin,  or  pewter,  are  not  dipped  into  acid 
before  plating,  but  into  a  strong  and  boiling-hot  solution  of 
pure  caustic  potash,  and  are  then  either  '  scratch-brushed ' 
or  taken  direct  from  the  alkali,  without  rinsing  in  water, 
and  immersed  in  a  cyanide  of  silver  solution  (at  about 
190°  Fahr.),  containing  a  considerable  proportion  of  free 
cyanide,  with  a  large  anode;  and  an  electric  current  of 
considerable  intensity,  is  passed  through  the  vat  for  several 
minutes,  until  the  articles  receive  a  thin  coating,  they  are 
then  transferred  to  the  ordinary  plating  solution,  to  receive 
the  full  amount  of  deposit :  steel  articles,  after  being  cleaned 
in  the  hot  potash,  are  dipped  (without  brushing)  into  a  solu- 
tion of  one  pound  of  cyanide  of  potassium  in  a  gallon  of 
water;  and  then  coated  thinly  with  silver  in  a  similar  manner, 
before  plating.  Those  of  lead  are  first  scraped,  or  otherwise 
made  quite  clean  and  bright,  by  mechanical  means,  and  then 
treated  in  the  same  manner  as  those  of  Britannia-metal. 
Articles  of  copper,  brass,  or  german-silver,  after  being  pro- 
perly cleansed,  are  dipped  into  the  solution  of  nitrate  of 


Electro-  Silvering  Base  Metals,  163 

mercury  (see  p.  166),  or  a  very  dilute  one  of  cyanide  of  mer- 
cury and  potassium  (pp.  95  and  323),  then  rinsed  in  a  vessel 
of  water,  and  immediately  suspended  in  the  depositing  vat. 
The  preparation  of  articles  by  immersion  in  a  bath  of  cyanide 
of  mercury  \\as  patented  by  Dr.  H.  B.  Leeson,  June  4.  1842, 
and  is  in  use  by  the  electro-platers  of  Birmingham.  If  the 
articles  ar,e  immersed  without  this  precaution,  the  deposited 
silver  does  not  always  adhere  firmly.  All  articles  are  attached 
to  the  cathode,  immediately  after  immersion  in  the  plating 
liquid. 

For  preparing  articles  of  tin,  lead,  zinc,  Britannia-metal, 
&c.,  a  cold  solution  is  sometimes  employed,  containing  from 
two  to  three  pounds  of  cyanide  of  potassium,  and  only  two 
to  five  pennyweights  of  silver  per  gallon ;  and  the  current 
from  the  usual  battery  is  passed  into  it  by  means  of  a  small 
anode,  But,  for  coating  steel  direct  with  a  preparatory 
film  of  silver  in  this  solution,  a  powerful  battery  is  used,  so 
as  to  evolve  hydrogen  from  the  steel  surface,  and  the  anode 
is  composed  of  a  large  sheet  of  platinum  together  with  a 
small  sheet  of  silver. 

For  silvering  cast-iron,  Bottger  recommends  a  bath  com- 
posed of  fifteen  parts  of  argentic  nitrate  dissolved  in  250  parts 
of  water,  to  which  thirty  parts  of  cyanide  of  potassium  have 
been  added.  After  complete  solution,  pour  the  mixture 
into  750  parts  of  water  containing  fifteen  of  common  salt. 
The  cast-iron  articles,  after  being  well  cleansed,  should  be 
placed  for  a  few  minutes  in  nitric  acid  of  sp.  gr.  1-2,  then 
rinsed  thoroughly,  and  placed  in  the  electro-depositing 
liquid. 

Brass,  copper,  or  nickel  articles,  also  those  of  iron  and 
zinc  which  have  been  coppered,  may  after  thorough  cleansing, 
be  silvered,  by  treatment  with  a  solution  of  fourteen  grammes 
of  silver  dissolved  in  twenty-six  grammes  of  nitric  acid,  to 
which  (after  the  silver  is  all  dissolved)  is  added  a  solution 
of  1 20  grammes  of  cyanide  of  potassium  in  one  litre  of  water, 
and  also  twenty-eight  grammes  of  finely  powdered  chalk. 

M  2 


164  The  A  rt  of  Electro-Metallurgy. 

The  original  paper  gives  further  directions  for  producing  dif- 
ferent shades  of  colour  on  the  silvered  articles  (C.  Paul, 
*  Journal  of  Chemical  Society/  vol.  xi.  p.  955). 

To  electro-plate  over  soft  solder. — Clean  the  articles  well 
with  alkali,  then  dip  them  in  red  nitrous  acid,  and  thoroughly 
rinse  away  all  the  traces  of  acid.  Dip  the  soldered  portion 
for  a  short  time,  in  a  very  dilute  solution  of  cyanide  of  mer- 
cury and  potassium  (see  p.  321).  Rinse  them  again,  and 
then  place  them  in  the  plating  vat 

In  addition  to  cyanide  mixtures,  other  solutions  have 
been  employed  for  electro-plating  by  the  separate  current 
process ;  amongst  which  the  most  practical  ones  are  those 
containing  the  sulphite,  or  the  hyposulphite  of  silver.  To 
form  the  first  of  these,  the  patentee  (Mr.  Woolrich)  directs  as 
follows : — '  Take  of  the  best  pearlash  of  commerce,  twenty- 
eight  pounds,  and  add  to  it  thirty  pounds  of  water,  and  boil 
them  in  an  iron  vessel  until  the  pearlash  is  dissolved  ;  the 
solution  should  then  be  poured  into  an  earthenware  or  other 
suitable  vessel,  and  suffered  to  stand  until  the  liquor  becomes 
cold.  It  should  then  be  filtered,  and  fourteen  pounds  of 
distilled  water  added ;  sulphurous  acid  gas  (obtained  by 
any  of  the  known  processes)  should  then  be  passed  into 
the  filtered  liquor  until  it  is  saturated,  taking  care  not  to  add 
the  gas  in  excess.  The  liquor  should  be  again  filtered,  and 
the  liquid  so  filtered,  is  what  I  term  the  solvent,  or  sulphite 
of  potash.' 

'  To  make  the  silvering  liquor,  which  I  use  in  coating 
with  silver  the  surface  of  articles  formed  of  metal  or  metallic 
alloys  :  I  dissolve  twelve  ounces  of  crystallised  nitrate  of 
silver  in  three  pounds  of  distilled  water,  in  a  clean  earthen- 
ware vessel,  and  add  to  the  solution,  by  a  little  at  a  time,  the 
before  mentioned  solvent,  so  long  as  a  whitish-coloured  de- 
posit is  produced  ;  care  being  taken  not  to  add  more  of  the 
solvent  than  is  necessary.  After  the  precipitate  has  subsided, 
I  pour  off  the  supernatant  liquor,  and  wash  the  sediment 
with  distilled  water.  To  the  precipitate  I  add  as  much  of 


Silver  Plating'  Solution  by  the  Battery  Process.    165 

the  before  mentioned  solvent  as  will  dissolve  it,  and 
afterwards  add  about  one-sixth  part  more,  so  that  the 
solvent  may  be  in  excess  ;  I  then  stir  them  well  together, 
and  let  them  remain  about  twenty-four  hours,  and  then  filter 
the  solution,  when  it  will  be  ready  for  use.  This  is  what  I 
designate  silvering  liquor '  ('  Repertory  of  Patent  Inventions,' 
5th  series,  1843,  p.  210).  This  liquid  is  a  very  good 
one,  except  that  it  gradually  decomposes  and  deposits  its 
silver,  by  the  influence  of  light. 

The  simplest  way  of  forming  the  hyposulphite  plating 
liquid,  is  by  dissolving  chloride  of  silver  in  a  solution  of 
crystals  of  hyposulphite  of  sodium.  The  liquid  yields  its 
metal  easily  by  means  of  the  electric  current,  but  under  the 
influence  of  light  it  is  decomposed,  and  its  silver  falls  to  the 
bottom  in  the  form  of  sulphide. 

Mr.  Alexander  Parkes  also  took  out  a  patent,  October  29, 
1 844,  for  depositing  silver  by  means  of  a  battery  and  a  silver 
anode,  from  melted  chloride  or  iodide  of  silver,  with  or  with- 
out the  addition  of  from  half  to  one  and  a  half  times  its 
weight  of  iodide  of  potassium,  to  increase  the  bulk  of  the 
liquid  ;  and  for  gilding  in  a  fused  mixture  of  two  parts  of 
iodide  of  gold  and  eight  parts  of  iodide  of  potassium ;  but 
neither  process  appears  to  have  been  much  used. 

Mixtures  composed  of  cyanide  of  silver  dissolved  in  solu- 
tions of  ferro-cyanide  of  potassium,  in  the  proportion  of  one 
ounce  of  silver,  to  three  pounds  of  the  cyanide,  have  also  been 
employed  for  plating,  and  yield  with  a  feeble  current,  an  ex- 
cellent deposit  of  soft  silver,  but  the  silver  anode  becomes 
covered  with  an  insoluble  white  crust,  which  falls  off,  and 
the  solution  soon  becomes  exhausted  of  metal. 

Making  silver  plating  liquid  by  battery  process. — The  or- 
dinary cyanide  of  silver  plating  solution  may  very  conve- 
niently be  made  by  the  battery,  process,  and  by  some  platers 
this  plan  is  preferred  to  all  others.  To  make  by  this  method, 
a  solution  containing  one  ounce  of  silver  per  gallon — first 
ascertain  the  percentage  of  actual  cyanide  in  the  salt  of 


1 66  The  A  rt  of  Electro-Metallurgy. 

potassium  to  be  used.  If  it  contains  about  50  percent,  dis- 
solve about  three  ounces  of  it  in  each  gallon  (=160  ounces) 
of  distilled  water  ;  or  if  it  contains  more,  add  less,  and  if 
less,  add  more,  in  proportion.  Suspend  a  large  anode  and 
a  small  cathode  of  silver,  in  the  liquid;  and  pass  a  strong 
current  of  electricity,  until  about  one  ounce  of  silver  for  each 
gallon  of  liquid  has  dissolved  from  the  anode,  or  until  with 
a  moderate  current,  and  electrodes  of  average  size,  a  bright 
silver  or  other  suitable  cathode,  receives  a  good  deposit.  As 
this  process  produces  some  caustic  potash  in  the  liquid, 
some  of  the  strongest  hydrocyanic  acid  may  now  be  added 
to  form  cyanide,  and  some  more  silver  then  dissolved  in 
the  mixture  by  the  battery  process. 

Condensed  outline  of  the  silver  plating  process. — (According 
to  the  French  method.)  Immerse  the  articles  of  copper, 
brass,  or  german- silver,  during  a  few  minutes,  in  a  boiling 
solution  of  one  part  of  caustic  potash  in  ten  parts  of  water. 
Swill  them  thoroughly  in  clean  water.  Dip  them  into  a 
liquid,  composed  of  ten  parts  of  water,  and  one  of  sulphuric 
acid.  Rinse  them  again.  Immerse  them  during  a  few 
seconds  in  a  mixture  of  twenty  parts  of  common  salt,  twenty 
of  calcined  soot,  and  1000  of  yellow  nitric  acid  of  specific 
gravity  1*332,  and  swill  them  as  quickly  as  possible  in  plenty 
of  water.  Dip  them  also  rapidly  in  a  mixture  (prepared 
some  time  beforehand)  of  one  part  of  sulphuric  acid,  sp.  gr. 
1*846,  forty  of  common  salt,  and  1000  of  yellow  nitric  acid, 
of  specific  gravity  1-332  ;  and  instantly  wash  them  well  in 
clean  water.  Dip  them  at  once  for  a  few  seconds,  or  until 
they  are  quite  white,  in  a  '  quicking '  solution,  composed 
of  ten  parts  of  nitrate  of  binoxide  of  mercury,  and  1000  parts 
of  water  containing  sufficient  sulphuric  acid  to  make  the 
solution  clear;  and  swill  them  again  in  the  fresh  water. 
Immerse  them  in  the  plating  liquid,  using  a  weak  current, 
and  if  the  deposit  looks  good,  continue  the  process,  but 
if  it  looks  uneven  or  spotted,  take  them  out, '  scratch-brush  ' 
them,  dip  them  into  a  hot  solution  of  cyanide  of  potassium, 


Bright  Silver  Deposition.  167 

and  then  in  fresh  water ;  '  quick '  them  afresh,  rinse  them 
again,  and  then  continue  the  process.  When  the  plating  is 
finished,  stop  the  current  a  few  minutes,  before  removing  the 
articles,  in  order  to  remove  subsalts  of  silver  from  the 
deposit,  and  prevent  its  turning  yellow.  Swill  them  in 
water,  then  in  water  slightly  acidified  by  sulphuric  acid, 
again  finally  in  water,  scratch-brush  them  if  necessary,  swill 
them  again,  dry  them  in  hot  sawdust  of  boxwood,  and  weigh 
them. 

Bright  silver  deposition. — The  history  of  the  discovery 
of  this  kind  of  plating  has  already  been  given  (see  pp.  26, 
27).  The  brightening  effect  is  produced  by  attending  to  the 
following  directions.  Take  one  quart  of  ordinary  cyanide 
of  silver  plating  liquid,  old  liquid  by  preference,  containing 
two  pounds  of  cyanide  of  potassium  per  gallon,  add  to  it 
four  ounces  of  strong  liquor  ammonia,  four  of  bisulphide  of 
carbon,  and  two  of  ether,  and  shake  it  occasionally.  After 
it  has  stood  twenty-four  hours,  add  two  ounces  of  the  super- 
natant liquid,  to  20  gallons  of  ordinary  silver  plating  solu- 
tion, with  gentle  stirring,  every  alternate  day.  Or  add  it 
every  day,  during  the  morning  in  summer,  and  evening  in 
winter.  But  in  every  case  it  is  highly  important,  to  add 
only  the  least  possible  quantity  necessary  to  produce  the 
effect ;  for  a  greater  number  of  silver  plating  solutions  have 
been  spoiled,  by  addition  of  an  excess  of  brightening  liquid, 
than  by  all  other  causes  put  together.  If  too  much  '  bright '  is 
added,  the  plated  articles  become  of  a  brown  colour,  and  fre- 
quently spotted.  The  bisulphide  of  carbon  mixture  gradually 
becomes  nearly  black  ;  it  may  stand  an  indefinite  length  of 
time,  and  as  often  as  two  ounces  of  the  supernatant  liquid  is 
taken  out,  an  equal  volume  of  old  plating  solution  strong  in 
cyanide,  or  a  strong  solution  of  cyanide  alone,  should  be 
added  ;  this  gradually  decreases  its  blackness,  and  also  pre- 
vents its  producing  a  precipitate  when  added  to  the  solution 
in  the  vat. 

Messrs.  Lyons  and  W.  Milward,  the  patentees  of  the  pro- 


1 68  The  A  rt  of  Electro-Metallurgy. 

cess,  give  in  their  patent  of  March  23, 1847,  the  following  in- 
structions for  forming  a  *  bright  solution.'  '  Add  to  the  usual 
solution  of  silver  in  cyanide  of  potassium,  bisulphide  of 
carbon,  terchloride  or  other  chloride  of  carbon,  sesqui- 
chloride  of  sulphur,  or  hyposulphite  of  either  potash  or  soda. 
The  bisulphide  of  carbon  may  be  used  alone,  or  dissolved  in 
sulphuric  ether  ;  or  it  may  be  used  in  conjunction  with  any 
of  the  other  substances  mentioned  above.  But  the  patentees 
prefer  using  it  as  follows : — Six  ounces  of  bisulphide  of 
carbon  are  put  into  a  stoppered  bottle,  and  one  gallon  of  the 
usual  plating  liquid  added  to  it ;  the  mixture  is  then  shaken 
and  set  aside  for  twenty-four  hours  ;  two  ounces  of  the  re- 
sulting solution  are  then  added  to  every  twenty  gallons  of  the 
ordinary  plating  solution  in  the  vat,  and  the  whole  stirred 
together;  this  proportion  must  be  added  every  day,  on 
account  of  the  loss  by  evaporation  ;  but  when  the  mixture 
has  been  made  several  days,  less  than  this  may  be  used 
at  a  time;  (when  hydrocarbons  are  used  instead  of  the 
bisulphide,  a  much  larger  quantity  must  be  added.) 
This  proportion  gives  a  bright  deposit,  but  by  adding  a 
larger  amount,  a  dead  surface  may  be  obtained  very  dif- 
ferent to  the  ordinary  dead  surface.'  This  substance  is 
generally  employed  throughout  the  trade.  Other  com- 
pounds have  also  been  used,  but  to  a  very  limited  extent ; 
among  these  are  sulphur  and  collodion.  A  solution  of 
iodine  and  gutta-percha  in  chloroform  is  said  to  be  more  per- 
manent in  its  effect  than  the  bisulphide  of  carbon.  Also  one 
and  a  half  ounces  each,  of  the  carbonate  and  acid  carbonate 
of  potassium,  added  once  in  nine  or  ten  days,  to  a  plating 
liquid,  containing  twelve  ounces  of  cyanide  of  potassium, 
and  three  and  a  half  of  silver  per  gallon,  is  said  to  produce 
the  same  effect.  But  these  do  not  equal  the  bisulphide. 
(M.  Plante  silvers  brightly,  by  adding  a  little  sulphide  of 
silver  to  the  bath.)  The  brightening  liquid  is  added  to  the 
ordinary  silver  cyanide  plating  solution,  and  the  proportion 
either  of  silver  or  of  free  cyanide,  per  gallon,  is  not  a  matter 


Vats  for  containing  Silver  Solutions.         169 

of  much  importance.     The  liquid  in  a  brightening  vat  is 
always  slightly  cloudy. 

Articles  in  the  brightening  solution  become  plated  more 
slowly  than  in  the  ordinary  plating  liquid.  They  commence 
to  become  bright  first  at  their  lower  parts,  and  become 
wholly  bright  in  about  fifteen  minutes.  The  '  bright '  vat  is 
only  used  to  'finish'  articles  in,  because  its  only  service  is 
to  impart  a  superficial  appearance.  The  electric  current 
required,  is  stronger  than  that  for  ordinary  silver  plating. 
Silver  deposited  from  a  brightening  solution  is  not  however 
pure  silver.  I  have  found  sulphur  in  it,  by  dissolving  it  in 
pure  dilute  nitric  acid,  determining  the  amount  of  silver, 
and  testing  for  sulphuric  acid,  in  two  separate  portions. 
Bright  silver  is  also  harder  than  that  deposited  from  the 
ordinary  cyanide  solutions,  and  has  very  much  the  appear- 
ance of  fused  metal.  If  there  are  very  small  holes  in  the 
surface  of  the  bright  articles,  dull  streaks  appear  above 
them.  Silver  deposited  in  bright  vats,  blackens  quickly  on 
removal  from  the  liquid,  unless  immersed  in  boiling  water 
for  a  short  time. 

Vats  for  con  faming  silver  solutions. — These  are  of  various 
dimensions  and  proportions,  but  usually  they  are  about  six  feet 
long,  three  feet  wide,  and  nearly  three  feet  deep  ;  and  they 
often  contain  200  or  300  gallons  of  the  liquid.  They  are  made 
of  different  materials ;  some  are  composed  of  wood  only, 
others  of  two  thicknesses  of  wood  with  lead  between  ;  but  the 
use  of  wooden  vats  is  nearly  discontinued,  because  they  absorb 
a  large  quantity  of  the  solution,  become  saturated  with  it, 
and  it  soaks  through  to  the  outside.  A  lining  of  gutta- 
percha  cannot  be  employed,  because  cyanide  of  potassium 
acts  upon  the  joints  of  that  substance.  They  are  now  made  of 
wrought  iron,  sometimes  with  a  thin  layer  of  wood  as  a  lining 
upon  the  sides  to  prevent  the  anodes  touching  them,  or  they 
are  lined  entirely  with  cement,  but  the  cement  yields  up  a 
little  impurity  (probably  oxide  of  iron)  to  the  liquid. 

Each  vat  has  a  wooden  rim  securely  fixed  to  its  upoer 


The  Art  of  Electro-Metallurgy. 

edge  all  round  it ;  upon  this  rim  is  fixed  a  rectangle  of  brass 
tubing  (see  annexed  sketch,  Fig.  23)  an  inch  in  diameter,  to 
which  is  soldered  a  large  binding-screw,  for  connection  with 
the  positive  pole  of  the  battery.  Within  this  rectangle  of 
tubing  is  also  similarly  fixed,  but  insulated  from  the  first  one, 
a  smaller  rectangle  of  brass-tubing,  about  half  an  inch  in  dia- 
meter, with  a  screw  for  connection  with  the  negative  pole. 
Cross  tubes  of  brass,  about  half  an  inch  in  diameter  and  as 

FIG.  23. 


long  as  the  vat  is  wide,  are  laid  in  clean  metallic  contact 
upon  the  larger  rectangle,  and  these  cross  tubes  support,  and 
are  metallically  connected  with  the  large  and  flat  sheet  silver 
anodes,  by  means  of  frames  of  iron,  which  extend  downwards 
into  the  liquid.  Similar,  but  shorter  brass  tubes,  are  laid 
across  the  vat,  with  their  ends  upon  the  inner  rectangle,  and 
these  support,  by  means  of  wires,  the  articles  to  be  coated. 
All  the  points  of  contact  of  the  cross  tubes  with  the  rect- 
angles, the  supporting  frames  and  wires  with  the  cross  tubes, 


Suspending  Articles  for  Plating. 


171 


and  the  other  connections,  are  frequently  examined,  and  kept 
scrupulously  clean,  by  means  of  rubbing  with  emery  cloth. 

The  wires  for  supporting  the  articles  are  usually  formed 
of  copper  about  the  thickness  of  bell-wire,  and  are  protected 
(excepting  their  ends  and  those  parts  which  are  not  im- 
mersed in  the  liquid)  from  receiving  a  useless  deposit  of 
silver,  by  enclosing  them  in  short  tubes  of  glass,  gutta- 
percha,  or  pure  india-rubber  ;  and  are  bent  at  their  lower 
ends  into  a  sort  of  a  loop,  when  required  to  support  forks  or 
spoons,  so  that  those  articles  may  be  readily  slipped  into  the 
loops  and  supported.  (See  Figs.  24,  25.) 


FIG.  24. 


FIG.  25. 


In  vats  where  the  articles  are  kept  in  continual  motion, 
the  cross  rods  supporting  them  are  fixed  to  an  iron  frame, 
with  four  small  wheels  (about  three  inches  diameter),  which 
move  backwards  and  forwards  to  an  extent  of  three  or  four 
inches  upon  inclined  rails  fixed  upon  the  edges  of  the  vat, 
and  impart  to  the  articles  a  combined  vertical  and  horizontal 
swinging  motion,  or  they  are  suspended  from  a  swinging- 
frame.  (See  Fig.  26,  p.  174.) 

Quality  of  the  deposited  silver. — The  quality  of  the  de- 
posited silver,  like  that  of  all  other  metals,  depends  chiefly 
upon  two  circumstances,  viz.  the  strength  of  the  current  in 


1 7  2  The  A  rt  of  Electro-Metallurgy. 

relation  to  the  magnitude  of  surface  of  the  article  to  be 
coated,  and  the  composition  and  temperature  of  the  plating 
solution.  If  the  articles  become  grey  or  black  in  the  solu- 
tion, and  evolve  much  gas,  the  current  is  too  strong,  and 
either  the  number  of  battery  cells,  or  the  depth  of  immer- 
sion of  the  battery-plates,  must  be  diminished.  If  the  de- 
posit is  good,  but  not  sufficiently  rapid,  it  is  best  increased 
by  greater  surface  of  immersion  of  the  battery-plates. 

Management  of  cyanide  plating  solutions. — Cyanide  of 
silver  plating  liquid  is  more  easily  managed  than  cyanide 
gilding  solution,  and  less  easily  than  the  ordinary  sulphate 
solution  employed  in  depositing  copper. 

There  are  various  circumstances  which  must  be  attended 
to,  in  order  to  keep  a  cyanide  plating  liquid  in  proper 
condition  for  yielding  a  good  and  suitable  deposit  of  silver, 
and  to  restore  it  to  that  state  when  it  has  changed  from 
it.  A  new  silver  solution  does  not  usually  work  as  well  as 
an  old  one,  provided  the  latter  is  not  too  old.  Solutions  which 
are  two  or  three  years  old  work  very  well,  but  those  which 
have  been  in  use  ten  or  twelve  years,  often  work  badly, 
because  they  generally  by  that  time  become  too  impure. 

Cyanide  plating  solutions  are  liable  to  change  from 
several  circumstances.  They  become  dirty  with  sus- 
pended solid  particles.  They  become  more  concen- 
trated, and  of  greater  density,  by  evaporation  of  water,  addi- 
tion of  cyanide  of  potassium,  increased  proportion  of  silver, 
&c.  They  either  increase  or  decrease  in  their  proportions 
of  silver  or  cyanide  by  various  causes ;  if  that  of  cyanide 
of  potassium  to  silver  is  large,  or  if  the  anode  is  large 
in  relation  to  the  receiving  surfaces,  the  proportion  of 
silver  increases,  and  of  free  cyanide  decreases ;  if  the  anode 
is  relatively  small,  reverse  effects  take  place.  They  acquire 
various  metals  besides  silver,  in  solution,  by  corroding 
articles  immersed  in  them  to  be  plated,  and  also  by  dissolv- 
ing impurities  from  the  anode.  They  gradually  decompose, 
become  brown,  and  evolve  ammonia  by  exposure  to  light, 


Management  of  Cyanide  Plating  Solutions.     173 

especially  if  they  contain  much  free  cyanide.  They  become 
spoiled  by  addition  of  too  much  brightening  liquid  ;and  so  on. 

If  the  solution  contains  suspended  solid  particles,  or 
sediment  which  is  liable  to  rise  by  the  motion  of  the  liquid, 
the  impurities  settle  upon  the  receiving  surfaces,  and  produce 
a  rough  or  uneven  deposit,  with  vertical  streaks  ascending 
from  them,  especially  if  the  articles  are  still,  the  liquid 
dense,  and  the  deposition  rapid.  Solutions  should  therefore 
be  filtered  when  necessary. 

If  the  liquid  is  too  dense,  the  articles  still,  and  deposi- 
tion is  rapidly  occurring,  the  goods  are  liable  to  become 
covered  with  vertical  streaks,  and  to  receive  a  much  thicker 
deposit  upon  their  lower  parts  than  upon  their  upper 
ones.  If  the  density  is  due  to  foreign  salts,  crystals 
of  those  salts  are  liable  to  form  upon  the  articles  in  cold 
weather,  and  spoil  the  deposit.  The  specific  gravity  of  a 
cyanide  plating  solution,  may  vary  from  1*036  to  1*116 
without  detriment  to  the  quality  of  the  deposited  metal, 
provided  the  greater  density  is  not  due  to  sparingly  soluble 
substances  ;  if  the  density  is  greater  than  this,  water  may  be 
added.  The  specific  gravity  of  an  old  plating  solution, 
analysed  by  me,  was  1*1821  at  65°  Fahr. ;  it  contained  16960 
grains  of  solid  matter  (including  499  grains  of  silver),  per 
gallon.  If  the  solution  contains  too  little  water,  but  has 
the  silver  and  cyanide  in  their  proper  relative  proportions,  it 
conducts  freely,  and  gives  a  good  and  quick  deposit;  but 
is  more  difficult  to  manage  than  a  weaker  liquid,  especially 
in  hot  weather,  because,  from  the  less  mobility  of  its  particles, 
it  is  more  apt  to  settle  into  strata  of  different  specific 
gravities  ;  its  lower  layers  become  nearly  saturated  with 
silver,  and  destitute  of  free  cyanide,  and  its  upper  ones 
become  exhausted  of  silver,  and  strongly  charged  with  free 
cyanide.  In  consequence  of  this,  the  upper  parts  .of  the 
anode  dissolve  rapidly,  whilst  the  upper  parts  of  the  articles 
receive  very  little  deposit,  and  the  lower  parts  of  them  are 
coated  too  rapidly,  and  neither  receive  a  deposit  of  the  best 


The  Art  of  Electro-Metallurgy. 

quality.  All  these  evil  effects  may  be  diminished  in  such  a 
solution,  by  stirring  it  well  every  night,  after  having  finished 
plating,  or  they  may  be  entirely  prevented  by  diluting  the 
liquid  to  a  proper  degree,  and  stirring  it  every  evening.  If 
the  solution  is  too  weak  (i.e.  contains  too  much  water),  it 
conducts  sparingly,  deposits  slowly,  and  the  deposit  has  a 
*  dead  '  white  appearance.  This  may  be  easily  remedied  by 
adding  cyanide  of  silver  and  cyanide  of  potassium  to  it  in 
proper  proportions,  and  working  it  uniformly  during  a  few 

FIG.  26. 


days.  The  evil  effects  of  improper  degree  of  density  of 
the  solution  upon  the  quality  of  the  deposited  metal,  may 
be  diminished,  by  keeping  the  articles  in  a  state  of  gentle 
motion,  by  means  of  an  apparatus  (such  as  is  shewn  in  Fig. 
26) ;  driven  by  power  from  a  steam-engine. 

If  the  anode  is  dirty,  it  indicates  a  deficiency  of  cyanide 
of  potassium:  this  may  be  remedied  by  adding  that  sub- 
stance ;  but  if  the  liquid  contains  much  carbonate  of  potas- 


Management  of  Cyanide  Plating  Solutions.     175 

sium,  as  it  usually  does,  either  as  an  impurity  of  the  cyanide 
employed,  or  by  decomposition  of  the  cyanide  by  light,  as 
in  a  brown  old  solution,  it  may  be  remedied  by  addition  of 
hydrocyanic  acid,  which  will  convert  the  carbonate  into 
cyanide.  The  necessity  of  adding  a  little  fresh  cyanide  is 
indicated,  when  the  dissolving  plate  begins  to  change  from 
its  ordinary  pure  white  appearance  to  a  dull  yellowish  grey 
colour.  It  is  best  added  in  the  evening  after  plating,  about 
half  an  hour  before  stirring  the  solution. 

If  the  anode  appears  grey  during  the  passage  of  the 
current,  and  white  whilst  the  current  is  stopped ;  and  if  in 
addition  to  this,  the  deposit  of  metal  is  good,  the  solution  is 
usually  in  propercondition.  But  if  the  anode  is  dark  coloured 
or  black  whilst  the  current  is  passing,  there  is  probably  either 
too  small  a  proportion  of  cyanide  of  potassium,  or  too  large  a 
one  of  silver ;  but  if  it  is  white,  the  reverse.  If  the  cold 
solution  coats  bright  copper  rapidly  with  silver  by  simple 
immersion  only,  it  probably  contains  too  much  free  cyanide 
of  potassium  •  a  bath  should  not  produce  this  effect  without 
the  aid  of  a  separate  current.  A  solution  containing  much 
free  cyanide,  causes  the  anodes  to  corrode  in  holes,  and  fall  to 
pieces,  especially  if  the  anodes  touch  the  iron  vat ;  it  also 
becomes  rapidly  richer  in  silver,  and  thus  cures  its  own  defect. 
The  proportion  of  free  cyanide  may  vary  greatly  without 
much  injury  to  the  solution,  or  to  the  quality  of  the  deposited 
metal.  One  part  of  good  cyanide  of  potassium  is  sufficient 
to  dissolve  one  part  of  silver  when  converted  into  cyanide  ; 
but  unless  there  is,  in  addition  to  the  quantity  actually  re- 
quisite to  retain  the  silver  in  solution,  a  considerable  excess 
of  free  cyanide  of  potassium,  the  conduction  is  defective, 
and  the  deposit  granular  and  irregular. 

To  quickly  ascertain  if  the  plating  liquid  contains  the 
proper  proportion  of  silver  to  cyanide  : — Put  twenty-five 
parts  by  weight  of  the  solution  into  a  tall  glass,  and  add  to  it, 
at  first  freely,  but  towards  the  last,  drop  by  drop,  with  con- 
stant stirring,  a  solution  of  one  part  of  crystallised  argentic 


1 76  The  A  rt  of  Electro-Metallurgy. 

nitrate  in  ten  parts  of  water.  If  the  precipitate  formed  dissolves 
rapidly,  with  but  little  need  of  stirring,  there  is  too  little  silver 
or  too  much  cyanide.  If  it  does  not  all  dissolve,  even  after 
much  stirring,  there  is  too  little  cyanide,  or  too  much  silver, 
but  if  it  wholly  dissolves  (the  latter  portions  quite  slowly), 
the  proportion  of  silver  to  cyanide  is  about  correct. 

If  a  solution  contains  a  great  excess  of  free  cyanide,  and 
is  also  deficient  in  water,  it  becomes  in  hot  weather  very 
difficult  to  manage,  and  emits  strongly  the  odours  of 
ammonia  and  hydrocyanic  acid.  In  such  a  solution,  if 
from  any  cause  the  battery  current  becomes  suddenly  weak 
towards  the  evening,  the  silver  deposited  upon  the  articles 
will  be  re-dissolved,  in  consequence  of  the  liquid  about 
the  anodes,  having  by  the  day's  work,  become  saturated 
with  silver,  and  that  about  the  articles,  become  full  of  free 
cyanide  ;  the  two  electrodes  (i.e.  the  dissolving  plates  and  the 
articles)  form  a  kind  of  voltaic  battery,  (of  one  metal  in  two 
liquids,  see  p.  69),  which  develops  a  current  of  electricity  in 
an  opposite  direction  to  the  original  one,  and  thus  re-dissolves 
the  deposited  silver.  (See  *  Polarization  of  electrodes/  p.  54.) 

On  some  rare  occasions,  gas  rises  freely  from  the  silver 
dissolving  plate  alone,  and  when  this  occurs,  if  the  plate  and 
articles  are  disconnected  from  the  battery,  and  the  ends  of 
the  wires  brought  into  contact,  and  then  suddenly  separated, 
a  minute  spark  (visible  in  the  dark),  is  seen,  produced  by  a 
current  opposite  in  direction  to  that  of  the  battery  current, 
and  probably  produced  by  some  polar  conditions  of  the 
dissolving  and  receiving  surfaces.  This  will  even  occur 
when  the  articles  are  kept  in  constant  motion,  and  even 
after  the  dissolving  plate  has  been  taken  out  of  the  liquid, 
and  re-immersed  after  the  lapse  of  half  an  hour.  On  such 
occasion?  there  is  a  tendency  to  a  gritty  deposit,  and  the 
solution  is  said  to  be  out  of  order.  (See  p.  54.) 

Peculiar  phenomena  often  occur  in  the  electro-deposi- 
tion of  silver,  not  only  upon  different  metals,  but  also  upon 
the  same  metals  in  different  forms,  or  under  other  conditions 


Management  of  Cyanide  Plating  Liquids.        177 

of  surface.  For  instance,  if  two  perfectly  similar  pieces  of 
thin  sheet  brass  are  taken  (except,  that  one  is  perforated  all 
over  with  small  holes),  and  both  be  simultaneously  immersed 
in  the  same  solution  to  be  silvered,  and  with  the  same 
battery  power  applied  to  each,  the  latter,  although  its  amount 
of  surface  is  reduced  by  the  perforations,  is  said  to  become 
coated  with  silver  much  more  slowly  than  the  former.  If  a 
wire  gauze  cylinder  of  a  Davy  lamp,  be  suspended  side  by 
side  with  a  piece  of  thin  tubing  of  the  same  metal,  and  of  the 
same  dimensions,  the  latter  will  become  coated  much  more 
rapidly  than  the  former.  If  two  pieces  of  the  same  metal, 
iron  for  instance,  be  immersed  to  be  silvered  in  the  ordinary 
cyanide  solution,  or  to  be  coppered  in  the  hot  cyanide 
of  copper  and  potassium  liquid,  each  containing  exactly  the 
same  amount  of  surface  to  be  coated,  but  one  being  in  the 
form  of  a  thin  sheet,  and  the  other  in  that  of  a  thick  plate, 
or  solid  block  of  metal,  the  former  will  become  coated 
much  more  rapidly  than  the  latter.  The  edges  and  points 
of  .articles,  "whilst  being  plated,  exhibit  a  greater  tendency  to 
a  crystalline  deposit  than  the  flat  parts,  and  this  tendency 
is  sometimes  manifested  in  depositing  silver  upon  table 
knives  and  forks.  It  is  the  knowledge  of  these,  and  many 
other  peculiarities,  of  different  metals  and  articles  met  with 
in  practical  working,  and  of  the  means  of  overcoming  their  at- 
tendant difficulties,  which  constitutes  one  of  the  chief  differ- 
ences between  the  practical  operator,  and  the  theoretical  man. 
Electro-deposited  silver  is  sometimes  of  a  yellow  colour, 
and  occasionally  pinkish ;  these  colours  are  due  to  impurities. 
The  yellow  appearance,  which  silver  deposited  from  a  cyanide 
solution,  sometimes  assumes  after  having  been  out  of  the 
liquid,  is  said  to  be  due  to  subcyanide  of  silver  in  the  deposit, 
and  the  pinkish  tint  is  probably  due  to  copper.  Liquid 
ammonia,  added  to  cyanide  of  silver  plating  solution  not 
containing  much  free  cyanide  of  potassium,  frequently  im- 
proves the  colour  of  the  deposit,  and  the  condition  of  the 
liquid. 

N 


The  Art  of  Electro-Metallurgy. 

A  bright  solution  is  much  more  difficult  to  manage 
than  the  ordinary  silver  liquid ;  if  it  is  not  worked  constantly, 
and  in  an  uniform  manner,  it  will  lose  its  power  of  yielding 
bright  metal.  If  any  of  the  articles  which  are  being 
plated  in  it  are  disturbed,  or  removed  from  the  liquid  and  re- 
placed, those  will  not  now  receive  a  bright  deposit,  and  the 
disturbance  of  the  liquid  by  their  removal,  will  oftentimes 
cause  all  the  neighbouring  articles  to  lose  their  brightness. 
If  too  much  '  brightening  liquid '  is  added,  the  solution  will 
be  considerably  injured ;  many  silver  solutions  have  been 
irretrievably  damaged  in  this  way.  A  bright  solution 
requires  a  battery  current  of  large  quantity  to  work  it,  and 
the  dissolving  plates  in  it  are  generally  of  a  darker  colour 
than  those  in  the  ordinary  silvering  liquid. 

Rapidity  of  silver  deposition. — The  rapidity  with  which 
metal  of  good  quality  can  be  deposited,  depends  largely 
upon  the  composition  of  the  solution.  To  work  rapidly, 
the  solution  should  contain  a  rather  large  proportion  of 
free  cyanide  of  potassium,  otherwise,  the  anode  becomes 
covered  with  an  insoluble  film,  before  free  cyanide  from  the 
articles  can  diffuse  to  it,  and  this  film  impedes  the  current. 
In  a  good  silver  solution,  a  dozen  of  ordinary  table  spoons 
or  forks  will  acquire  1000  to  1500  grains  of  silver  in  twelve 
hours,  but  there  are  solutions  used  in  Birmingham,  in  which 
it  is  said  as  much  as  one  ounce  of  silver  can  be  deposited 
upon  a  small  table  spoon  in  half  a  day. 

Thickness  of  deposited  silver. — Electro-plated  articles  vary 
greatly  in  quality,  because. any  degree  of  thinness  of  silver 
may  be  put  upon  them.  Great  quantities  of  Britannia-metal 
articles  are  coated  with  only  a  few  pennyweights  of  silver 
per  square  foot.  '  The  thickness  of  electro-deposited  silver 
is  in  many  cases  from  TVnol  to  ¥Jotb,  or  even  Wire^1  °f  a 
millimetre,  or  1-24  grains  upon  a  square  metre  of  surface.' 
One  ounce  of  silver  per  square  foot  of  surface,  is  equal  to  a 
coating  of  about  the  thickness  of  thin  writing-paper,  and 
is  considered  an  excellent  coating.  The  prominent  parts  of 


Thickness  of  Deposited  Silver.  179 

a  plated  article  usually  receive  the  thickest  coating,  because 
electricity  enters  and  leaves  the  projecting  parts  of  bodies 
more  readily  than  their  hollow  parts,  and  in  deposition  the 
prominences  of  the  anode  receive  the  most  perfect  supply  of 
free  cyanide,  and  those  of  the  cathode  receive  chiefly  the 
supply  of  saturated  solution.  '  M.  M.  Christofle,  during  the 
year  1865,  deposited  33,600  kilogrammes  of  silver,  upon 
5,600,000  objects  ;  and  covered  a  surface  of  112,000  square 
metres,  with  three  grammes  of  silver  upon  each  square  centi- 
metre.' 

'In  France,  electro-plating  is  regulated  by  law,  every 
manufacturer  being  required  to  weigh  each  article  when 
ready  for  plating,  in  the  presence  of  a  comptroller  appointed 
by  the  Government,  and  to  report  the  same  article  for 
weighing  again  when  the  plating  has  been  done.  In  this 
way,  the  comptroller  knows  to  the  fraction  of  a  grain,  the 
amount  of  precious  metal  that  has-been  added,  and  puts 
his  mark  upon  the  wares  accordingly,  so  that  every  pur- 
chaser, may  know  at  a  glance,  what  he  is  buying.  As  to  the 
amount  of  silver  consumed  in  ordinary  plating — an  ounce 
and  a  half  of  silver  will  give  to  a  surface  a  foot  square,  a  coat- 
ing as  thick  as  common  writing-paper,  and,  since  silver  is 
worth  five  shillings  per  ounce,  the  value  of  the  silver  covering 
a  foot  square,  would  be  about  seven-and-sixpence.  At  this 
rate,  a  tea-pot  or  coffee-pot  is  well  plated,  at  a  cost  in  silver, 
of  not  more  than  seven  or  eight  shillings.  The  other  expenses, 
including  labour,  would  hardly  be  more  than  half  that  amount. 

'  The  popular  notion  is,  that  genuine  electro-gilding 
must  necessarily  add  a  good  deal  to  the  cost  of  the  article 
coated.  This  is  erroneous.  A  silver  thimble  may  be 
handsonrely  coated,  so  as  to  have  the  appearance  of  being 
all  gold,  for  threepence,  a  pencil  case  for  tenpence,  and  a 
watch  case  for  four  shillings.  An  estimate  of  the  relative 
value  of  electro-gilding  as  compared  with  silver  plating, 
considering  the  cost  of  material  alone,  is  about  five  to  one. 
The  quantity  of  silver  used  in  plating  the  wares  sent  in  such 

N  2 


1 80  The  A  rt  of  Electro-Metallurgy, 

large  quantities  to  the  colonies,  is  about  an  ounce  to  the 
square  mile  \  one  hard  cleaning  exposes  the  base  metal,  and 
your  bargain  from  auction  or  cheap  store,  may  be  thrown 
on  the  dust  heap J  ('  Technologist ').  In  Birmingham  iron 
snuffers  are  sometimes  'silvered'  wholesale,  at  as  low  a 
price  as  fourpence  per  pair  ;  and  hooks  and  eyes,  at  one 
penny  per  pound. 

In  England  also,  the  articles  are  weighed  both  before  and 
after  plating  ;  some  French  electro-platers  use  a  '  plating 
balance,'  the  articles  being  suspended  from  one  end  of  the 
beam,  and  a  scale  pan  containing  weights  from  the  other, 
by  means  of  which,  when  the  articles  have  received  any 
desired  amount  of  deposit  (determined  beforehand),  the 
circuit  is  automatically  broken,  and  the  deposition  stopped. 

The  average  cost  of  depositing  silver  has  been  estimated 
at  twopence  per  ounce,  but  this  would  probably  only  include 
the  cost  of  the  battery  power,  and  not  of  the  numerous  other 
incidental  expenses.  A  very  large  amount  of  plating  is  done, 
at  a  cost  of  about  eight  shillings  per  ounce  of  deposited  silver, 
by  professed  electro-platers  (*  electro-platers  to  the  trade  '), 
whose  sole  occupation  is  electro-deposition,  for  others,  who 
are  called  '  electro-platers.  Many  manufacturers  of  spoons, 
forks,  tea-pots,  coffee-pots  and  other  articles,  have  at  different 
times  commenced  to  plate  for  themselves,  but  have  found, 
that  the  coated  articles  were  so  often  required  to  be  stripped 
and  re-plated,  and  that  the  difficulties  and  incidental  ex- 
penses were  so  great,  that  they  have  abandoned  the  actual 
performance  of  the  process,  and  send  the  articles  to  the 
regular  '  electro-platers  to  the  trade  '  to  be  done. 

Ornamenting  silver  articles.  Dead  silver;  '  Oxidised 
silver' — Frequently,  for  the  purposes  of  ornamentation,  and 
of  producing  a  pleasing  effect,  the  surface  of  deposited 
silver  is  treated  in  various  ways.  To  obtain  what  is  termed 
a  '  dead '  appearance,  like  frosted  silver,  deposit  a  mere 
trace  of  copper  upon  it  in  a  sulphate  of  copper  solution, 
and  then  a  very  thin  layer  of  silver  upon  that.  '  Oxidised ' 


Ornamenting  Silver- Plated  A  r tides.  1 8 1 

silver,  is  not  silver  coated  with  oxide,  but  with  a  film  of 
platinum,  or  of  sulphide  of  silver  ;  the  former  is  produced, 
by  applying  a  hot  solution  of  perchloride  of  platinum,  and 
allowing  it  to  dry  ;  the  colour  varies  from  a  light  steel-grey 
to  nearly  black.  The  hotter  the  solution,  and  the  greater 
proportion  of  platinum  in  it,  the  deeper  black  does  it  pro- 
duce. The  colour  arises  from  finely  divided  black  metallic 
platinum,  deposited  by  simple  immersion  process ;  and  the 
silver  is  slightly  corroded  by  the  action,  forming  chloride 
of  silver,  which  may  be  dissolved  by  means  of  diluted 
aqueous  ammonia.  A  bluish  black  colour  is  produced  by 
means  of  a  freshly  made,  and  hot  solution,  of  sulphide  of 
potassium  ('liver  of  sulphur').  '  Nielled  silvering'  is  a 
process  of  sulphurising  engraved  parts  of  silver  surfaces, 
and  consists  in  inlaying  the  surface  with  sulphide  of  silver 
which  has  been  prepared  beforehand,  and  causing  it  to 
adhere  firmly  to  the  metal,  by  heating  the  article  in  a  muffle 
until  the  sulphide  melts.  This,  however,  is  a  separate  art, 
closely  allied  to  enamelling. 

To  produce  a  beautiful  pink  colour  upon  silver,  dip  the 
clean  article  for  a  few  seconds  in  a  hot  and  strong  solution 
of  cupric  chloride,  swill  it  in  water,  and  then  dry  it,  or  dip  it 
in  spirit  of  wine,  and  ignite  the  spirit.  (W.  H.  Fearn.) 

A  blackish  colour  is  sometimes  produced,  by  making  a 
thin  magma  of  plumbago  and  spirit  of  turpentine,  and 
nibbing  it  upon  the  surface.  After  drying,  the  black  is 
rubbed  off  from  the  prominent  parts  of  the  surface  by  means 
of  a  rag  wetted  with  alcohol ;  the  process  is  called  '  old  or 
antique  silvering.'  To  produce  a  brownish-black  colour  upon 
silver  articles,  a  solution,  composed  of  equal  weights  of  salam- 
moniac  and  sulphate  of  copper  dissolved  in  vinegar,  is  applied. 

Articles  of  silver  are  also  ornamented,  by  depositing 
gold  upon  portions  of  their  surfaces;  and  those  of  gold  are 
ornamented,  by  depositing  gold  of  different  tints  of  colour 
(sometimes  as  many  as  five  or  six)  upon  their  different 
parts ;  this  is  effected  by  covering  the  parts  which  are  not 


1 82  The  A  rt  of  Electro-Metallurgy. 

to  receive  the  coating,  with  a  varnish  which  will  resist  the 
solvent  power  of  the  hot  alkaline  gilding  liquid.  The  com- 
position of  such  a  varnish  is  as  follows  :— 

Translucent  resin  ......  10  parts 

Yellow  beeswax     .         ...         .         .  6     ,, 

Extra  line  red  sealing-wax      .         .         .         .  4     ,, 

The  finest  polishing  rouge  (i.  e.  impalpable  per- 
oxide of  iron)    .         .         .         .         .  3     ,, 

Best  quick  drying  copal  varnish,  with  some  peroxide  of 
iron,  or  ultramarine,  mixed  with  it,  is  used  for  '  stopping  off/ 
in  hot  cyanide  solutions,  or  mixed  with  chromate  of  lead,  if 
for  use  in  cold  liquids.  It  dries  in  about  three  or  four  hours. 

Cleaning  silver. — A  yellow  colour  upon  silver  which  has 
been  electro-deposited,  is  said  to  be  due  to  the  action  of  the 
air  upon  a  basic  or  subcyanide  of  silver  in  the  pores  of 
the  metal,  and  may  be  removed  by  immersing  the  article 
either  in  a  solution  of  cyanide  of  potassium,  or  in  ordinary 
plating  solution  containing  free  cyanide.  A  weak  solution 
of  cyanide  of  potassium  is  also  a  good  substance  to  clean 
discoloured  silver,  but  it  dissolves  a  little  silver,  and  is  also 
a  very  dangerous  liquid  to  be  entrusted  to  ignorant  persons, 
being  exceedingly  poisonous. 

The  East  Indian  jewellers  clean  silver,  by  briskly  rubbing 
it  with  slices  of  a  juicy  lemon,  and  then  covering  the  article 
with  the  slices  in  a  pan  for  a  few  hours.  They  then  swill 
them  two  or  three  times  in  water  ;  stir  them  in  nearly  boiling 
soap-suds,  brush,  rinse,  and  finally  dry  them  on  a  metal 
plate  over  hot  water.  Green  tamarind  stems  are  more  power- 
fully detergent  than  lemons,  and  are  employed  to  remove 
oxide  and  fire  marks  from  gold  and  silver  ('Telegraphic 
Journal,'  vol.  xi.  p.  178).  Silver  may  be  cleaned  in  water  in 
which  potatoes  have  been  boiled,  and  a  superior  polish  is 
thus  imparted  to  them  (Eisner,  '  Chemical  Society's  Journal,' 
vol.  xi.  1072).  A  good  polishing  paste  for  silver,  is  composed 
of  washed  whiting,  precipitated  carbonate  of  magnesia,  and 
precipitated  peroxide  of  iron. 


Stripping  Plated  A  rticles.  1 83 

c  Stripping '  articles. — Sometimes,  articles  composed  of 
copper,  brass,  or  german-silver,  which  have  been  plated 
with  a  portion  of  silver,  require  to  have  the  coating  entirely 
removed,  and  a  new  deposit  put  upon  them,  because 
the  first  was  defective.  Occasionally  also,  the  depositor  has 
sent  to  him.  to  be  re-plated,  old  articles  of  silvered  copper, 
('  Sheffield  plate,')  the  coating  upon  which  has  partly  worn 
away;  these  require  to  have  the  remaining  portions  of 
silver  removed,  in  order  to  obtain  a  uniform  surface 
to  deposit  upon.  The  removal  of  the  silver  is  termed 
*  stripping.'  To  effect  this,  add  a  very  little  nitrate  of  soda 
('  Chili  saltpetre,')  to  a  quantity  of  strong  and  hot  oil  of 
vitriol,  and  immerse  the  articles  in  the  mixture,  until  all  the 
silver  is  dissolved.  If  the  action  becomes  slow,  apply  more 
heat,  and  add  more  saltpetre  at  the  moment  of  using.  The 
copper  will  not  be  much  acted  upon,  if  the  articles  are  not 
allowed  to  remain  in  too  long.  A  number  of  such  articles 
are  generally  '  stripped '  together,  and  are  afterwards  washed, 
and  prepared  in  the  usual  manner  for  receiving  a  deposit;  or 
the  silver  may  be  removed,  but  more  slowly,  without  the  aid 
of  heat,  by  suspending  the  articles  for  a  greater  or  less  length 
of  time,  according  to  the  thickness  of  the  coating,  in  a  bulky 
mixture  of  ten  measures  of  strong  sulphuric  acid,  and  one 
measure  of  concentrated  nitric  acid,  contained  in  a  large 
stoneware  vessel.  The  liquid  must  not  be  diluted,  but  be 
kept  as  free  from  water  as  possible,  by  not  immersing  wet 
articles  in  it,  and  by  keeping  it  covered  from  the  air  ;  other- 
wise it  will  attack  the  copper,  brass,  bronze,  or  german- 
silver  base  of  the  articles.  As  the  liquid  becomes  weaker, 
very  small  portions  of  strong  nitric  acid  are  added  to  it.  Its 
action  is  less  rapid  than  that  of  the  hot  mixture  already  de- 
scribed. In  stripping  an  article  for  re-plating,  the  whole  of 
the  silver  should  be  taken  off,  otherwise  the  deposit  sub- 
sequently put  upon  it,  is  apt  to  shew  lines,  where  silvered 
and  unsilvered  portions  meet.  Some  depositers  re-plate 
defectively  coated  articles  without  stripping  them ;  they 


1 84  The  A  rt  of  Electro- Metallurgy. 

merely  well  '  scratch-brush/  'buff,'  and  'quick'  them  re- 
peatedly, and  then  put  on  the  second  coating  ;  but  this  is  a 
less  satisfactory  method. 

If  the  base  of  the  article  is  composed  of  iron,  steel,  zinc, 
or  lead,  the  above  mode  of  stripping  by  acids  is  not  applic- 
able, and  the  coating  is  best  removed,  by  making  the  articles 
the  anode,  in  an  ordinary  cyanide  of  silver  plating  solution, 
until  the  silver  is  dissolved. 

Sometimes  it  is  necessary  to  perform  the  converse  opera- 
tion, viz.  to  strip  copper  from  the  surface  of  silver,  as  when 
a  thin  copper  mould  has  to  be  removed  from  a  solid  deposit 
of  silver  formed  upon  it  by  electro-plating  process.  To  effect 
this,  boil  the  article  in  dilute  hydrochloric  acid,  or  immerse 
it  in  a  hot  solution  of  perchloride  of  iron.  This  latter  liquid 
may  be  made  by  digesting  peroxide  of  iron  (crocus,  or  jewel- 
ler's rouge)  in  warm  hydrochloric  acid,  as  long  as  it  will 
dissolve  ;  the  solution  will  remove  tin,  lead,  or  copper,  from 
either  gold  or  silver,  without  affecting  those  metals.  A 
solution  of  chloride  of  zinc  has  been  used  for  the  same  pur- 
pose. Copper  may  also  be  completely  removed  from  silver 
or  gold,  by  making  it  the  anode  in  a  sulphate  of  copper  solu- 
tion, until  all  the  copper  is  dissolved  ;  the  silver  will  remain 
unaffected  if  the  current  employed  is  feeble,  and  has  not 
a  greater  intensity  than  one  or  two  pairs. 

Sometimes  articles  of  silver  which  are  gilded,  require  to 
have  the  gold  removed  from  them ;  this  is  effected  by  heat- 
ing them  to  redness,  and  throwing  them  into  dilute  sulphuric 
acid ;  the  gold  scales  off  in  spangles,  and  falls  to  the  bottom. 
The  process  is  repeated  until  all  the  gold  is  removed.  With 
articles  which  are  hollow,  it  is  better  to  make  them  the  anode 
in  a  solution  of  one  part  of  cyanide  of  potassium  and  ten 
parts  of  water,  with  a  cathode  of  platinum. 

Analysts  of  cyanide  of  silver  plating  solutions. — The  only 
points  usually  required  to  be  known  respecting  the  compo- 
sition of  a  silver  plating  liquid,  are  the  proportions  of  free 
cyanide  of  potassium,  and  of  metallic  silver. 


Analysis  of  Plating  Solutions.  185 

The  common  method  of  ascertaining  the  percentage  of 
free  cyanide,  is  that  of  Glassford  and  Napier,  and  may  be 
carried  out  as  follows  : — Dissolve  a  known  weight,  say  fifty 
grains  of  crystallised  nitrate  of  silver,  in  distilled  water,  and 
dilute  it  to  a  known  weight  or  bulk.  Take  a  known  measure 
of  the  plating  liquid,  say  one  ounce,  if  it  is  not  extremely 
strong  in  free  cyanide.  Add  the  solution  of  nitrate  to  the 
plating  liquid,  just  as  long  as  the  precipitate  formed  dissolves 
completely  on  stirring,  and  ascertain  how  much  of  the  silver 
salt  has  been  consumed.  Every  170  parts  of  nitrate,  equal 
130-2  parts  of  free  cyanide. 

The  silver  of  an  old  cyanide  plating  solution,  cannot  be 
satisfactorily  converted  into  pure  chloride,  by  adding  an  ex- 
cess of  hydrochloric  acid,  and  boiling  the  mixture  ;  the  pre- 
cipitate so  obtained  is  of  varied  colours,  and  contains  foreign 
substances.  To  ascertain  the  amount  of  silver,  evaporate  a 
known  volume  of  the  solution  to  dryness,  fuse  the  residue  at 
a  red  heat  in  a  porcelain  crucible,  cool  it,  and  dissolve  the 
saline  residue  in  water  (testing  the  water  for  silver  by  means 
of  hydrochloric  acid),  taking  care  to  collect  any  chloride 
of  silver  present  Dissolve  the  metallic  residue  in  warm 
dilute  nitric  acid ;  and  estimate  the  amount  of  silver  in  the 
solution,  by  ordinary  volumetric  or  gravimetric  methods. 
The  silver  may  also  be  estimated  as  follows,  by  a  method  I 
have  employed.  Take  700  grains  by  measure  of  the  solu- 
tion •  evaporate  it  to  dryness  ;  add  sixty  grains  of  sulphate, 
and  fifteen  of  nitrate  of  ammonium,  both  in  powder,  mix,  and 
dry  thoroughly.  Transfer  the  mixture  to  a  capacious  porce- 
lain crucible,  and  heat  very  gradually  to  fusion  at  a  low  red 
heat.  Dissolve  the  cooled  residue  in  hot  dilute  nitric  acid, 
taking  care  to  collect  any  undissolved  chloride  of  silver. 
Precipitate  the  dissolved  silver  by  hydrochloric  acid,  filter, 
wash,  ignite,  and  weigh  the  pure  argentic  chloride,  every 
143*5  Parts  of  which  equal  108  parts  of  silver.  In  this  pro- 
cess, all  the  cyanogen  of  the  solution,  is  expelled  by  the 
fusion  with  the  sulphate  and  nitrate  of  ammonium,  and  the 


1 86  The  A  rt  of  Electro-Metallurgy. 

base  metals  and  alkalies  are  converted  into  soluble  sulphates. 
Frequently  the  fused  saline  mass  is  quite  green  with  copper 
and  other  metals.  A  sample  of  plating  solution,  analysed  by 
this  method,  gave  147-54 grains  of  metallic  silver  per  gallon, 
and  much  copper  ;  another  yielded  499-2  grains,  and  a 
great  quantity  of  chlorides  ;  a  third  1,720  grains,  and 
much  copper,  iron,  and  chlorides  ;  seven  others  gave 
from  348-1  to  979-9  grains  ;  six,  from  1,701  to  2,195 
grains;  and  eight  yielded  from  519  to  865  grains  per 
gallon. 

According  to  G.  C.  Wittstein,  cyanide  of  silver  plating 
solution  may  be  completely  analysed  as  follows  : — i.  Mix 
twenty  cubic  centimetres  of  the  liquid  with  fourteen  cc.  of 
acetic  acid  of  20  per  cent. ;  evaporate  ;  extract  the  residue 
with  absolute  alcohol ;  evaporate  the  alcoholic  solution  ;  heat 
the  residue  with  hydrochloric  acid ;  dry,  and  weigh  as  chloride 
of  potassium  (KC1).  This  gives  the  total  amount  of  potas- 
sium (K)  as  free  cyanide,  as  potassic  silver  cyanide,  car- 
bonate, and  cyanate. 

2.  Take  a  second  twenty  cc.  of  the  solution,  add  sulphide 
of  ammonium — (NH4)2S — in  slight  excess,  find  amount  of  ar- 
gentic sulphide,  and  calculate  from  it  the  amount  of  potassium 
in  the  double  cyanide  (KCy  AgCy). 

3.  Precipitate  a  known  portion  of  the   plating  liquid 
with  calcic  chloride,  and  weigh  the  carbonate  of  calcium 
(Ca  CO3) ;  this  gives  by  calculation  the  amount  of  potassic 
carbonate  (K2CO3). 

4.  As  the  impure  cyanide  contains  for  every  seven  equi- 
valents of  cyanide  of  potassium,  three  equivalents  of  cyanate 
(7  KCy  +  3  CyKO),  calculate  from  this  and  the  other  data, 
the  amount  of  potassic  cyanate. 

And,  5.  Deducting  from  the  entire  amount  of  potassic 
chloride  obtained  in  No.  i,  the  quantity  of  the  same  salt 
equivalent  to  the  amount  of  double  cyanide  (KCyAgCy), 
the  potassic  carbonate  and  potassic  cyanate  ;  the  remainder, 
is  the  amount  of  potassic  chloride,  equivalent  to  the  quantity 


Recovering  Gold  and  Silver  from  Old  Solutions.  187 

of  free  cyanide  of  potassium  in  the  solution  ('Journal  of  the 
Chemical  Society,'  vol.  xii.  p.  1012). 

Napier  (commenting  on  Wittstein's  process)  recommends 
a  simpler  one  as  follows  : — To  find  the  amount  of  silver,  eva- 
porate one  ounce  of  the  solution  to  dryness,  and  fuse  the  dry 
residue  in  a  small  crucible.  Dissolve  the  saline  mass,  ob- 
tain the  little  button  of  silver,  and  weigh  it;  or,  precipitate  one 
ounce  of  the  solution,  by  hydrochloric  acid  in  excess  ;  wash, 
dry,  and  weigh  the  product  :  three-fourths  of  the  weight  of 
which  is  silver.  To  one  ounce  of  the  liquid,  add  a  solution 
of  nitrate  of  silver  as  long  as  a  cloud  is  produced  ;  wash  the 
precipitate  with  water  by  decantation  ;  add  to  it  an  excess 
of  a  mixture  of  equal  volumes  of  nitric  acid  and  water,  which, 
by  digestion,  dissolves  all  the  silver  salt  not  cyanide.  Decant 
the  liquid,  add  a  little  hydrochloric  acid  to  it,  wash,  dry,  and 
weigh  any  precipitated  chloride  of  silver.  One-half  of  the 
weight  of  this  precipitate,  approaches  closely  to  the  amount 
of  cyanate  or  carbonate  of  potassium,  the  difference  in  their 
equivalents  not  being  great.  If  there  was  any  chloride  in  the 
original  plating  solution,  the  chloride  of  silver  corresponding 
to  it,  will  remain  in  the  portion  of  precipitate  insoluble  in  the 
dilute  nitric  acid. 

Recovering  silver  and  gold  from  residuary  liquids,  &v.1 — 
Many  silver  plating  solutions  are  spoiled  by  unsuccessful 
attempts  to  improve  them  ;  by  the  accidental  introduction  of 
impurities ;  by  adding  excess  of  cyanide  of  potassium;  by  having 
been  improperly  made;  and  especially  by  addition  of  too  much 
'  brightening  liquid ; '  and  we  wish  to  recover  their  metal. 
There  are  two  general  modes  of  recovering  silver  from  worn- 
out  or  spoiled  solutions,  or  waste  residuary  liquids  :  one,  by 
precipitating  the  silver  as  chloride  by  addition  of  sufficient 
hydrochloric  acid,  washing  and  drying  the  chloride  of  silver 
precipitate,  and  fusing  it  with  carbonate  of  potassium  con- 
taining a  little  saltpetre  to  oxidise  the  baser  metals  ;  and  the 
other,  by  evaporating  the  solution  to  dryness,  and  fusing 
1  See  also  p.  145. 


1 83  The  A  rt  of  Electro-Metallurgy. 

the  product  without  the  addition  of  any  oxidising  substance, 
which  would  be  very  dangerous  if  cyanide  of  potassium  is 
present.  In  both  cases  the  silver  and  gold  are  set  free. 

To  recover  silver  from  '  stripping '  solution  in  the  form 
of  cyanide,  dilute  the  supernatant  liquid  with  water,  dissolve 
the  precipitated  yellow  powder,  or  crystals  of  sulphate  of 
silver,  by  addition  of  nitric  acid  to  the  water.  Pour  off 
the  clear  liquid,  and  add  cyanide  of  potassium  to  it  as  long 
as  a  precipitate  of  cyanide  of  silver  takes  place,  or  until  effer- 
vescence of  hydrocyanic  acid  occurs  by  decomposition  of 
the  excess  of  cyanide  of  potassium  by  the  free  nitric  and 
sulphuric  acid  present.  Collect,  wash,  and  dry  the  precipi- 
tated cyanide  of  silver  ;  and,  after  testing  the  liquid  portion 
with  hydrochloric  acid  to  see  if  it  contains  any  traces  of  silver, 
throw  it  away.  Another  plan  is  to  add  a  solution  of  wash- 
ing-soda to  the  '  stripping-liquid '  until  the  latter  is  alkaline 
to  red  litmus  paper  (i.e.  turns  the  paper  blue),  then  acidify 
the  mixture  by  addition  of  hydrochloric  acid.  After  sub- 
sidence, throw  away  the  clear  liquid,  dry  the  sediment,  and 
fuse  it  with  a  mixture  of  the  dried  carbonates  of  potassium 
and  sodium  containing  a  little  saltpetre.  The  nearly  pure 
silver  and  gold  remains. 

As  the  recovery  of  silver  and  gold  from  silvering  and 
gilding  solutions,  is  an  important  matter  in  practical  electro- 
metallurgy, I  extract  the  following  valuable  remarks  from  a 
paper  by  Eisner  :  '  I  have  undertaken  a  series  of  researches 
upon  this  object,  and  hasten  to  communicate  the  results 
to  the  public  ;  but,  before  proceeding  to  the  communication, 
I  think  it  necessary  to  mention  the  results  of  the  experiments, 
upon  which  are  based  the  methods  given  further  on,  for 
extracting  both  the  silver  and  the  gold  of  old  cyanide  of 
potassium  liquids. 

'  i.  If  we  add  hydrochloric  acid  to  a  solution  of  silver  in 
cyanide  of  potassium  until  the  liquid  exhibits  an  acid  re- 
action, we  obtain  a  white  precipitate  of  chloride  of  silver, 
which,  when  submitted  to  heat,  melts  into  a  yellow  mass. 


Recovering  Gold  and  Silver  from  Old  Solutions.  189 

If  this  was  cyanide  of  silver,  the  application  of  a  red  heat 
would  have  left  a  regulus  of  silver.  The  addition  of  the  hydro- 
chloric acid,  precipitates  all  the  silver  present  in  the  liquid  in 
the  form  of  chloride  of  silver. 

'  2.  If  we  evaporate  a  solution  of  silver  in  cyanide  of  po- 
tassium to  dryness,  and  heat  the  residue  to  redness,  until  the 
mass  is  in  a  state  of  quiet  fusion,  and  has  assumed  a  brown 
colour,  there  remains,  when  we  wash  the  mass  with  water, 
metallic  and  porous  silver.  The  wash  waters,  when  filtered, 
still  contain  a  little  silver  in  solution ;  because,  if  hydro- 
chloric acid  is  added  to  them,  it  produces  a  precipitate  of 
chloride  of  silver.  In  evaporating  and  calcining  a  solution 
of  gold  in  cyanide  of  potassium,  the  result  is  similar,  i.e.  we 
obtain  metallic  gold.  The  wash  waters,  acidulated  with 
hydrochloric  acid,  give,  when  treated  with  sulphuretted 
hydrogen,  a  brown  precipitate  of  sulphide  of  gold ;  and, 
with  the  salt  of  tin,  a  violet  precipitate  (purple  of  Cassius), — a 
proof  that  these  liquids  still  contain  a  little  gold  in  solution. 

'  3.  If  we  pour  upon  finely-divided  silver — for  instance, 
silver  leaf,  or  silver  precipitated  in  the  porous  state  by 
zinc,  from  a  solution  of  silver — a  concentrated  solution  of 
cyanide  of  potassium,  at  the  ordinary  temperature,  and  shake 
it  frequently,  the  liquid,  at  the  end  of  a  certain  time,  exhibits 
silver  in  solution,  and  by  adding  hydrochloric  acid  to  it,  we 
produce  an  abundant  precipitate  of  chloride  of  silver.  This 
experiment  explains  why,  in  the  wash  waters  of  the  various 
combinations  of  gold  or  silver  with  cyanide  of  potassium,  we 
can  still  demonstrate  the  presence  of  gold  and  of  silver  after 
the  most  minute  separation. 

'  4.  When  hydrochloric  acid,  or  ordinary  sulphuric  acid, 
is  added  to  a  solution  of  cyanide  of  copper  and  cyanide  of 
potassium,  until  the  liquid  exhibits  an  acid  reaction,  the 
result  is  a  reddish-white  precipitate,  which  is  a  cyanide  of 
copper  in  the  anhydrous  state.  If  the  precipitate  be  well 
washed,  and  boiled  in  potash  lye,  oxide  of  copper  is  sepa- 
rated, of  a  beautiful  red  colour ;  and  if  to  the  filtered  alka- 


< 


1 90  The  A  rt  of  Electro-Metallu  rgy. 

line  liquid  we  add  a  solution  of  green  copperas,  a  dirty-blue 
precipitate  is  obtained.  A  solution  of  carbonate  of  sodium 
furnishes  the  same  results,  and  yields  with  the  copperas,  the 
same  dirty-blue  precipitate.  If  the  reddish-white  pre- 
cipitate is  dissolved  in  pure  nitric  acid,  and  a  solution 
of  nitrate  of  silver  is  added  to  it,  an  abundant  white  pre- 
cipitate is  produced,  which,  when  washed,  dried,  and  cal- 
cined, yields  silver  in  the  metallic  state — a  proof  that  the 
precipitate  is  cyanide  of  silver.  The  reddish-white  preci- 
pitate is  soluble  in  an  excess  of  hydrochloric  acid,  in  nitric 
acid,  and  in  aqua  regia  ;  it  is  also  soluble  in  aqueous 
ammonia,  and  in  a  solution  of  cyanide  of  potassium. 

'  5.  When  a  solution  of  silver,  prepared  for  silvering  arti- 
cles of  bronze  or  of  brass,  has  been  employed  a  certain  time 
for  that  purpose,  the  precipitate  produced  in  it  by  the  addi- 
tion of  hydrochloric  acid  is  not  pure  white,  but  reddish,  in 
consequence  of  the  reddish-white  cyanide  of  copper  which 
is  precipitated  with  it  :  for  we  know  that  those  silvering 
liquids  which  have  been  used  for  some  time,  contain  copper 
in  solution.  The  same  thing  occurs  with  the  solutions  for 
gilding,  in  which  articles  of  silver,  copper,  bronze,  and  brass, 
have  been  gilded  for  a  long  time  ;  the  liquid  contains  after  a 
certain  time  of  service,  not  only  gold,  but  also  silver  and 
copper.  This  case  presents  itself  especially  when  gilded 
articles  of  silver,  containing  copper,  or  other  alloys  of  silver, 
are  in  the  solution  of  gold ;  then  the  precipitate  of  cyanide 
of  gold  produced  by  the  addition  of  hydrochloric  acid,  does 
not  possess  its  proper  pure  yellow  colour.  It  has  happened 
to  me  to  observe  a  precipitate  of  this  kind,  which,  instead  of 
being  yellow,  was  green,  and,  in  fact,  articles  of  iron  had 
been  gilded  in  the  solution,  and  the  precipitate  contained, 
besides  cyanide  of  gold,  Prussian  blue,  so  as  to  be  demon- 
strated in  an  examination,  which  consisted  in  boiling  the 
green  precipitate  in  aqua  regia,  filtering  to  separate  the  dirty- 
green  residue,  evaporating  the  filtered  liquid  to  dryness,  and 
dissolving  the  dry  salt  in  water  acidulated  with  hydrochloric 


Recovering  Gold  and  Silver  from  Old  Solutions.  191 

acid  ;  the  addition  of  sulphate  of  iron  to  this  new  liquid 
gave  a  brown  precipitate,  and  the  salts  of  tin  a  reddish -brown 
precipitate.  In  treating  by  aqua  regia,  the  cyanide  of  gold 
was  then  decomposed,  and  converted  into  chloride  of  gold . 

'  Based  upon  the  preceding  facts,  we  may  find  several 
methods  for  recovering  all  the  silver  and  gold  of  old  cyanide 
of  potassium  solutions.  The  extraction  of  these  precious 
metals  maybe  effected,  either  by  the  wet  or  by  the  dry  process. 

'  Extraction  of  silver  by  the  wet  method. — Adding  hydro- 
chloric acid  until  the  liquid  exhibits  a  strongly  acid  reaction. 
The  precipitate  of  chloride  of  silver  which  is  thus  obtained, 
will  be,  as  we  have  already  said,  of  a  reddish-white  colour, 
because  of  the  cyanide  of  copper,  which  is  precipitated  with 
it,  when  the  solution  has  been  used  a  long  time  for  silvering 
objects  containing  copper.  In  this  precipitation  by  hydro- 
chloric acid,  there  is  hydrocyanic  acid  gas  set  free,  therefore 
the  operation  should  only  be  performed  in  the  open  air,  or 
in  a  place  where  there  is  good  ventilation ;  if  the  precipitate 
is  very  red,  it  must  be  treated  with  hot  hydrochloric  acid, 
which  will  dissolve  the  cyanide  of  copper.  The  chloride  of 
silver,  having  been  washed  with  water,  must  be  dried,  and 
then  fused  with  pearlash  in  a  Hessian  crucible  coated  with 
borax,  in  the  ordinary  manner  for  obtaining  metallic  silver. 

*  This  method  is  very  simple  in  its  application,  and  very 
economical,  considering,  that  by  the  aid  of  the  hydrochloric 
acid,  all  the  silver  contained  in  the  solution  of  cyanide  of 
potassium  is  precipitated,  and  there  remains  no  trace  of  it 
in  the  liquid.  But  the  quantity  of  hydrocyanic  gas  which 
is  disengaged,  is  a  circumstance  which  must  be  taken  into 
serious  consideration  when  operating  on  large  quantities  of 
silver  solution,  the  vapour  of  which  is  most  deleterious,  and 
nothing  but  the  most  perfect  ventilation,  combined  with 
arrangements  for  the  escape  of  the  poisonous  gases,  will 
admit  of  the  process  being  carried  on  without  danger  to  the 
workmen ;  when,  however,  we  have  taken  the  precautions 
dictated  by  prudence,  the  method  in  question  may  be  con- 


1 92  The  A  rt  of  Electro- Metallurgy. 

sidered  as  perfectly  practical.  The  liquid  should  be  poured 
into  very  capacious  vessels,  because  the  addition  of  the  acid 
produces  a  large  amount  of  froth. 

'Extraction  of  silver  by  the  dry  method.  — The  solution  of 
cyanide  of  silver  and  potassium  is  evaporated  to  dryness, 
the  residue  fused  at  a  red  heat,  and  the  resulting  mass,  when 
cold,  is  washed  with  water.  The  remainder  is  the  silver  in  a 
porous  metallic  condition.  There  still  remains  in  the  wash 
waters  a  little  silver,  which  may  be  precipitated  by  the  addi- 
tion of  hydrochloric  acid. 

*  Extraction  of  gold  by  the  wet  method. — A  solution  of  gold 
and  cyanide  of  potassium,  which  has  long  served  for  gilding 
articles  of  silver  alloyed  with  copper,  may  still  contain,  as 
we  have  already  remarked,  independently  of  the  gold,  both 
silver  and  copper,  and  perhaps  iron.  In  order  to  obtain 
these  metals  we  operate  in  the  following  manner  : — 

'  The  liquid,  the  same  as  with  the  solution  of  silver,  is 
acidulated  with  hydrochloric  acid,  in  which  case  there  is 
produced  a  disengagement  of  hydrocyanic  acid  gas,  which 
requires  the  same  careful  ventilation.  This  addition  of 
hydrochloric  acid  causes  a  precipitate,  which  may,  according 
to  circumstances,  consist  of  cyanide  of  gold,  cyanide  of 
copper,  and  chloride  of  silver.  The  precipitate,  washed  and 
dried,  is  boiled  in  aqua  regia,  which  dissolves  the  gold  and 
copper  in  the  form  of  metallic  chlorides,  and  leaves  the 
chloride  of  silver  unaffected.  The  solution,  containing  the 
gold  and  the  copper,  is  evaporated  nearly  to  dryness,  in 
order  to  drive  off  any  excess  of  acid  ;  it  is  then  dissolved  in  a 
small  quantity  of  water,  and  the  gold  precipitated  from  it 
(by  the  addition  of  protosulphate  of  iron)  in  the  state  of  a 
brown  powder.  The  chloride  of  silver  is  reduced  to  the 
metallic  state  by  the  known  means.  The  liquid  from  which 
we  have  precipitated  the  cyanide  of  gold,  &c.,  by  hydrochloric 
aciJ,  may  yet  contain  a  little  gold  in  solution.  I  refer  to  No. 
5  for  its  further  treatment. 

This  method  is  distinguished  by  the  great  simplicity  of  the 


Extraction  of  Gold  from  Old  Solutions.       193 

operation,  and  we  may  repeat  for  it  all  that  we  have  already 
said  respecting  the  extraction  of  silver  by  the  wet  method. 

'  Extraction  of  gold  by  the  dry  method. — The  solution  of 
cyanide  of  potassium  which  contains  gold,  silver,  and  copper, 
is  evaporated  to  dryness ;  the  residue  fused  at  a  red  heat, 
cooled,  and  washed  (the  wash  waters  still  contain  a  little 
gold  and  silver,  and  this  occurs  most  often  when  the  solution 
of  gold  or  silver  contains  a  very  great  excess  of  cyanide  of 
potassium).  The  residue,  after  washing,  consists  of  gold  and 
silver  in  a  metallic  porous  state,  and  carbide  of  copper  re- 
sulting from  the  decomposition  of  cyanide  of  copper  by  the 
heat.  The  metallic  residue  is  treated  with  aqua  regia,  which 
forms  insoluble  chloride  of  silver,  and  contains  the  chlorides 
of  gold  and  copper  in  solution.  In  order  to  obtain  these 
bodies  in  the  metallic  state,  we  must  proceed  in  the 
manner  previously  indicated. 

'  If  we  operate  according  to  the  method  of  Professor 
Boettger,  i.e.  if  we  fuse  the  dried  residue  with  its  own  volume 
of  litharge,  in  a  covered  crucible,  the  regulus  we  obtain  in 
this  case,  consists  of  gold,  silver,  and  lead.  In  treating  this 
alloy  by  nitric  acid,  of  specific  gravity  1*2,  and  applying 
heat,  the  gold  remains  in  the  form  of  a  brown  powder, 
whilst  the  lead  and  the  silver  are  dissolved  in  the  acid.  This 
solution,  after  having  been  largely  diluted  with  boiling  dis- 
tilled water,  may  have  the  silver  separated  from  the  lead,  by 
the  addition  of  hydrochloric  acid. 

'  These  methods  of  extracting  the  silver  and  gold,  from  old 
solutions  of  cyanide  of  potassium  by  the  dry  process,  present 
this  advantage,  that  the  operator  is  not  incommoded  while 
working,  by  the  disengagement  of  vapours  of  hydrocyanic 
acid.  In  these  operations,  the  poisonous  gases  are  not  deve- 
loped as  they  are  in  the  processes  for  extracting  the  metals 
by  the  wet  method. 

'  After  the  experiments  here  reported,  those  who  are 
interested  in  the  subject,  may  choose  for  themselves,  which 
of  these  methods  appears  the  most  suitable  to  the  circum- 

o 


1 94  The  A  rt  of  Electro- Metallurgy. 

stances  in  which  they  are  placed,  and  the  object  which  they 
wish  to  obtain.' 

The  process  of  recovering  the  silver  from  old  plating 
solutions,  depends  largely  upon  the  bulk  of  the  liquid  ;  if  that 
is  srnall,  the  liquid  may  be  evaporated  to  dryness,  and  the 
silver  recovered  by  the  dry  method,  taking  care  to  ascertain 
that  the  fused  salt  above  the  button  of  silver,  is  free  from 
precious  metals,  before  throwing  it  away ;  but  if  the  bulk  is 
great,  the  solution,  contained  in  capacious  vessels,  must  be 
precipitated  by  an  excess  of  hydrochloric  acid,  added  to  it 
in  the  open  air,  taking  extreme  care  not  to  breathe  the  vapour 
of  hydrocyanic  acid  which  is  evolved. 

Testing  the  purity  of  silver. — The  silver  recovered  from 
solutions,  strippings,  and  residues,  is  often  not  pure  ;  that 
employed  as  anodes  is  sometimes  not  perfectly  pure,  and 
electro-deposited  silver,  although  not  often  alloyed,  is  not 
necessarily  pure,  because  in  some  cases,  other  metals  are  de- 
posited with  it,  in  order  to  obtain  the  desired  tint  of  colour. 

According  to  Dr.  Bottger,  the  purity  of  silver  may  be 
ascertained  as  follows  :— Apply,  by  means  of  a  glass  rod,  a 
drop  of  cold  saturated  solution  of  bichromate  of  potassium, 
in  nitric  acid  of  sp.  gr.  1-2,  to  a  clean  part  of  the  surface, 
and  immediately  wash  it  off  with  cold  water ;  if  the  silver  is 
pure,  a  blood-red  mark  is  left.  All  other  metals  behave  differ- 
ently from  this  ('Chemical  News/  vol.  xxiii.  p.  119).  Runge 
had  also  previously  employed  a  somewhat  similar  test.  He 
immersed  the  article  in  a  cold  mixture  of  thirty-two  parts  of 
water,  four  of  sulphuric  acid,  and  three  of  chromate  of  potash. 
The  immersed  part  quickly  assumed  a  purple  colour,  which 
was  less  deep  and  less  lively,  in  proportion  to  the  amount  of 
alloy  contained  in  the  silver. 

Silver  may  be  purified,  by  dissolving  it  in  warm  dilute 
nitric  acid,  immersing  clean  sheets  of  copper  in  the  liquid, 
until  all  the  silver  is  precipitated,  finally  making  the  solution 
quite  warm,  to  complete  the  precipitation,  or  until  a  little  of 
it  gives  no  white  cloud  on  adding  to  it  two  or  three  drops  of 


Preparation  of  Salts  of  Mercury.  1 9  5 

hydrochloric  acid.  The  liquid  may  then  be  thrown  away, 
the  metallic  silver  precipitate  washed,  dried,  and  melted,  with 
the  addition  of  a  little  carbonate  of  potassium,  and  a  trace 
of  saltpetre  put  with  it  into  the  crucible ;  or  the  silver  may  be 
preserved  for  future  use  in  making  argentic  nitrate.  Silver 
may  also  be  purified  by  dissolving  it  in  nitric  acid,  then 
precipitating  it  by  hydrochloric  acid,  and  fusing  the  washed 
and  dried  chloride,  with  about  one-half  its  weight  of  the  an- 
hydrous carbonates  of  sodium  and  potassium,  and  a  little 
saltpetre,  in  an  earthen  crucible. 

14.  Mercury. — Elec.  chern.  eqt.  =  ^^  =  100     The  or- 

2 

dinary  compounds  of  this  metal,  are  the  dioxide  (red  preci 
pitate),  nitrate,  mercurous  chloride  (calomel),  bichloride  or 
mercuric  chloride  (corrosive  sublimate),  bisulphide  (vermi- 
lion), and  bicyanide.     The  most  soluble  of  these  salts  are 
the  nitrate,  bichloride,  and  bicyanide. 

Mercuric  nitrate  is  made,  by  dissolving  mercury  in  diluted 
nitric  acid ;  corrosive  sublimate  may  be  more  conveniently 
purchased  than  made.  The  bicyanide  is  prepared,  by  add- 
ing eight  parts  of  Prussian  blue,  and  sixteen  parts  of  mercuric 
oxide  (red  precipitate),  (both  in  a  state  of  fine  powder,)  to 
thirty  parts  of  water;  boiling  the  mixture  about  fifteen 
minutes,  filtering,  evaporating,  and  crystallising  the  solution. 
It  may  also  be  made,  by  digesting  an  excess  of  red  oxide  of 
mercury,  in  the  strongest  aqueous  hydrocyanic  acid,  until  the 
odour  of  the  acid  has  disappeared,  and  then  evaporating  the 
clear  liquid.  Also  by  dissolving  one  part  of  ferro-cyanide 
of  potassium,  in  fifteen  of  boiling  water,  adding  two  parts 
of  mercuric  sulphate,  digesting  it  hot  for  fifteen  minutes, 
and  then  filtering  the  mixture,  and  crystallising  the  clear 
solution.  Lielegg  prepares  it,  by  passing  vapour  of  hydro- 
cyanic acid  through  water  in  which  finely  divided  oxide  of 
mercury  is  suspended  ('  Chemical  News,'  vol.  xxvi.  p.  264). 
About  fifty-five  grains  of  cyanide  of  mercury,  dissolve  in 
one  ounce  of  water  at  60°  Fahr.  I  have  found  that  two 


1 96  The  A  rt  of  Electro-Metallurgy. 

and  a  half  ounces  of  corrosive  sublimate,  converted  into 
oxide  of  mercury,  required  about  nine  ounces  of  hydrocyanic 
acid  of  maximum  strength  (i.e.  'Scheele's  strength,'  see  p. 
197)  to  dissolve  it  with  the  assistance  of  heat.  The  double 
cyanide  of  mercury  and  potassium  may  be  made,  by  dissolving 
an  equivalent  of  bicyanide  of  mercury  in  water  containing  an 
equivalent  of  cyanide  of  potassium  in  solution,  and  evapora- 
ting the  clear  liquid.  A  very  dilute  solution  of  this  salt,  is  used 
for  '  quicking'  the  surfaces  of  articles  of  copper,  brass,  and 
german-silver,  which  are  to  be  silver-plated.  (See  also  p.  323.) 

Deposition  of  mercury  by  simplt  immersion  process  (see 
also  p.  78). — From  solutions  of  mercuric  chloride,  cyanide, 
or  nitrate,  aluminium  deposits  mercury  ;  forming  an  amalgam 
which  decomposes  water  at  60°  Fahr.,  and  rapidly  oxi- 
dises and  becomes  heated  in  the  air.  Aluminium  deposits 
mercury  from  a  solution  of  mercuric  chloride  in  alcohol ;  also 
from  one  of  mercuric  iodide  in  potassic  iodide  (A.  Cossay 
*  Watts'  Dictionary  of  Chemistry,'  2nd  Supplement,  p.  54). 
From  a  solution  of  mercuric  chloride,  magnesium  deposits 
calomel  and  mercuric  oxide  (Commaille, '  Chemical  News,'  vol. 
xiv.  p.  1 88),  Nearly  all  the  base  metals  coat  themselves  with 
mercury  by  simple  immersion  in  solutions  of  mercuric  salts. 

Electrolysis  of  salts  of  mercury  (see  also  p.  89). — Com- 
paratively little  as  yet  has  been  done  in  the  electrolysis 
of  salts  of  mercury.  A  solution  of  any  such  salt  may  be 
electrolysed,  by  putting  some  mercury  as  an  anode  in  the 
bowl  of  a  tobacco  pipe,  thrusting  a  platinum  wire  down  the 
pipe  into  the  mercury,  and  immersing  the  bowl  in  the  liquid ; 
or  the  mercury  may  be  placed  in  the  vessel  which  contains 
the  solution,  and  be  connected  with  the  positive  pole  of  the  bat- 
tery by  a  platinum  wire  passing  through  a  tube  of  india-rubber 
to  protect  it  from  the  liquid.  Gladstone  and  Tribe  have  ob- 
served, that  on  passing  a  weak  electric  current  through  a  solu- 
tion of  mercuric  chloride,  into  a  cathode  of  platinum,  a  film 
of  mercurous  chloride  is  deposited ;  but  with  a  strong  electric 
current,  mercury  itself  is  set  free.  I  have  noticed,  that  with 


Electrolytic  Vibrations  and  Sounds.          197 

a  mercury  anode  and  platinum  cathode,  in  dilute  sulphuric 
acid,  the  cathode  soon  receives  a  coating  of  mercury  on 
passing  a  current. 

Electrolytic  vibrations  and  sounds. — As  long  ago  as  the 
year  1801,  Gerboin  observed,  that  mercury  exhibited 
peculiar  movements  whilst  acting  as  an  electrode  in  electro- 
lysis, and  this  phenomenon  has  been  since  investigated 
by  Sir  J.  Herschel,  Sir  H.  Davy,  and  others.  According  to 
G.  Lippmann,  the  contraction  of  a  globule  of  mercury, 
(whilst  acting  as  a  cathode  in  dilute  sulphuric  acid,)  on  the 
passage  of  the  current,  is  due  to  a  change  in  the  capillary 
constant  ('Journal  of  the  Chemical  Society/  vol.  xi.  p. 
1094).  It  was  whilst  investigating  these  peculiar  move- 
ments, and  searching  for  thermic  changes  in  electrolysis,  by 
passing  an  electric  current  through  a  solution  of  double 
cyanide  of  mercury  and  potassium,  with  mercury  electrodes, 
that  I  first  heard  a  faint  sound,  and  then  observed  the 
surface  of  the  mercury  covered  with  waves  ;  and  by  further 
research,  was  led  to  the  discovery  of  electrolytic  sounds  ;  the 
dancing  motion,  and  musical  sound,  being  due  to  the  alter- 
nate formation  and  destruction,  of  films  upon  the  mercury, 
by  electrolytic  action.  A  paper  on  the  subject  in  the 
1  Proceedings  of  the  Royal  Society'  1862,  contains  a  full 
account  of  the  phenomenon,  and  of  the  influence  of  various 
circumstances  upon  it. 

The  best  liquid  for  producing  the  sounds,  consists  of  ten 
grains  of  cyanide  of  mercury,  and  ioo  of  pure  hydrate  of 
potash,  dissolved  in  2|  ounces  of  aqueous  hydrocyanic  acid, 
containing  5  per  cent,  of  the  anhydrous  acid  ('  Scheele's 
strength ') ;  the  liquid  should  be  filtered.  The  phenomena 
usually  occur  only  at  the  negative  electrode ,  and  out  of 
a  large  number  of  solutions  examined,  the  only  ones  in  which 
phonetic  vibrations  occurred,  were  those  of  alkaline  cyanides 
containing  dissolved  mercury.  The  quicksilver  may  be 
contained  in  two  very  small  watch  glasses  submerged  in  the 
solution ;  and  the  current,  from  either  two  Grove's,  or  five 


198  The  A  rt  of  Electro- Metallurgy. 

Smee's  cells,  conveyed  to  the  electrodes  by  platinum  wires, 
protected,  except  at  the  ends,  from  contact  with  the  liquid 
by  means  of  tubes  of  glass  or  india-rubber.      During  the 
FIG.  27.          occurrence  of  the  sounds,  the  current  itself  is 
rendered  imperfectly  intermittent,    and    the 
arrangement  may  to  a  certain  extent  be  em- 
ployed for  similar  uses  to  those  of  a  break- 
hammer.     A  more  perfect  arrangement,  con- 
sists of  a  glass  vessel  of  the  annexed  form 
(see  fig.  27),  placed  upon  a  sounding-board. 
One  portion  of  mercury  is  poured  into  the 
centre,  the  other  into  the  annular  space,  the  wires  immersed 
the  two  portions,  and  the  liquid  is  above. 


CLASS   IV.     BASE   METALS. 

COPPER — NICKEL  —  COBALT  —  IRON —  MANGANESE  —  CHRO- 
MIUM   URANIUM  —  TUNGSTEN — MOLYBDENUM  —  VANA- 
DIUM— LEAD — THALLIUM — INDIUM  —  TIN — CADMIUM  — 
ZINC. 

15.  Copper.— Elec.-chem.  eqt  = -^-=  3175.       The 

commonest  salts  of  copper,  are  the  suboxide,  or  cupreous 
oxide  (red  oxide  of  copper) ;  the  protoxide,  or  cupric  oxide 
(black  oxide  of  copper)  ;  the  nitrate,  chloride,  sulphate  (blue 
vitriol),  cyanide,  and  acetate.  The  black  oxide  is  made  by 
heating  the  nitrate  to  full  redness  in  a  crucible,  washing  and 
drying  the  product.  The  sulphate  is  most  conveniently 
purchased  (its  price  is  about  sixpence  per  pound) ;  or  it 
may  be  made  by  heating  copper  filings  in  oil  of  vitriol  until 
the  product  is  nearly  dry,  washing  the  residue  in  boiling 
water,  evaporating  and  crystallising  the  filtered  solution. 
The  chloride  and  nitrate  may  be  formed,  the  first  by  dissolv- 
ing copper  in  aqua  regia,  or  by  saturating  hydrochloric  acid 
with  protoxide  of  copper,  and  evaporating  and  crystallising 
the  liquids  ;  and  the  second,  by  dissolving  copper  in  nitric 


Electrical  Relations  of  Copper.  199 

acid,  evaporating  and  crystallising  the  solution.  Acetate  of 
copper  is  most  conveniently  purchased  ;  its  commercial  name 
is  crystallised  verdigris.  Cyanide  of  copper  may  be  made, 
by  adding  a  solution  of  cyanide  of  potassium  to  one  of 
sulphate  of  copper  (each  liquid  being  cold),  just  as  long 
as  a  precipitate  is  produced,  but  no  longer ;  filtering  and 
washing  the  precipitate,  which  is  the  required  compound; 
it  is  a  fine  powder  of  a  pale  green  colour.  In  the  opera- 
tion, a  large  quantity  of  cyanogen  gas  is  evolved,  which 
if  inhaled  is  dangerous  to  health.  The  powder  contains 
two  equivalents  of  cyanogen,  for  every  three  equivalents  of 
copper  ;  it  is  freely  soluble  in  a  solution  <5f  cyanide  of 
potassium  ;  it  is  also  soluble  in  aqueous  ammonia,  and  in  a 
solution  of  carbonate  of  ammonium.  The  liquid,  after  pre- 
cipitation, is  invariably  greenish  blue,  and  contains  much 
dissolved  copper,  but  no  use  has  hitherto  been  made  of  this 
remainder.  Carbonate  of  copper  may  be  prepared,  by  pre- 
cipitating a  cold  solution  of  cupric  sulphate,  by  one  of 
washing-soda  ;  it  is  a  green  powder. 

Electrical  relations  of  copper. — Copper  is  electro-positive 
to  iron  in  the  following  liquids  at  60°  Fahr.  :  powerfully  in 
a  solution  of  sulphide  of  ammonium  ;  feebly  in  a  saturated 
aqueous  one  of  ammonia  ;  in  a  solution  of  oxide  of  copper 
in  liquid  ammonia,  in  aqueous  ammonia,  or  in  a  saturated 
solution  of  ferro-cyanide  of  potassium,  each  but  for  a  short 
time — it  then  becomes  negative  ;  in  a  saturated  solution  of 
bichromate  of  potassium  ;  in  a  strong  aqueous  one  of  sul- 
phide of  potassium,  it  is  increasingly  positive  up  to  the  boil- 
ing point  of  the  liquid.  This  last  liquid  has  a  similar  effect 
on  brass. 

Deposition  of  copper  by  simple  immersion  process  (see  also 
p.  78). — From  a  solution  of  cupric  sulphate,  magnesium 
deposits  the  metal,  its  hydrated  protoxide,  and  a  green 
subsalt;  but  from  one  of  cupric  chloride,  it  precipitates 
Brunswick-green  and  no  metal  (Commaille,  'Chemical 
News/  vol.  xiv.  p.  188).  Metallic  aluminium  immersed 


200  The  A  rt  of  Electro- Metallurgy. 

in  a  similar  solution,  very  slowly  deposits  copper ;  and, 
in  one  of  the  nitrate,  it  slowly  separates  (after  several 
days)  a  basic  salt  and  metallic  copper ;  the  reduction  is 
quicker  if  an  alkaline  chloride  is  added.  From  a  solution 
of  the  chloride,  it  quickly  deposits  copper,  but  from  one  of 
the  acetate,  the  copper  is  more  slowly  separated  (A.  Cossa, 
'Watts'  Dictionary  of  Chemistry,'  2nd  Supplement,  p. 
54).  By  adding  crystals  of  silicon  to  melted  black  oxide 
of  copper,  I  observed  a  sudden  incandescence,  which  raised 
the  temperature  to  a  full  white  heat ;  copper  was  also  de- 
posited and  melted  to  a  red  metallic  bead,  and  could  be 
hammered  into  a  thin  sheet.  By  heating  to  redness  also, 
one  part  of  fragments  of  magnesium  and  six  of  cupric 
fluoride,  copper  was  separated.  I  have  also  observed,  that 
crystals  of  silicon  immersed  in  a  solution  of  fluoride  of 
copper  containing  free  hydrofluoric  acid,  instantly  coat  them- 
selves with  bright  copper,  and  evolve  gas.  According  to 
Smee,  iron  does  not  decompose  a  neutral  solution  of  acetate 
of  copper,  nor  alkaline  ones  of  the  ammoniuret,  ammonio- 
nitrate,  or  ammonio-sulphate ;  but  decomposes  a  solution  of 
oxide  of  copper  in  nitric  acid.  Raoult  states,  that  gold  in 
contact  with  copper,  in  either  a  cold  or  boiling,  acid  or 
neutral,  solution  of  a  salt  of  copper,  receives  no  deposit  of 
copper  ('Journal  of  the  Chemical  Society,'  vol.  xi.  p.  465). 

Electrolysis  of  salts  of  copper. — I  have  electrolysed 
fluoride  of  copper  (fused  at  a  bright  red  heat  in  a  deep 
copper  vessel),  by  means  of  a  platinum  wire  helix  as  the 
anode,  and  a  copper  wire  helix  as  the  cathode,  and  a 
current  from  six  Smee's  cells.  The  conduction  was  copious, 
as  if  the  fused  salt  conducted  like  a  metal,  and  an  acid, 
vapour  was  evolved.  No  copper  was  deposited,  and 
the  anode  was  unaltered  ;  the  cathode  lost  3-35  grains 
in  weight,  by  corrosion  near  the  surface  of  the  fused  salt, 
and  the  copper  vessel  was  similarly  acted  upon  in  several 
experiments,  and  caused  to  leak.  It  was  evidently  an 
instance  of  conduction  by  a  liquid  without  electrolysis,  as 


Electrolysis  of  Salts  of  Copper.  2OI 

with  fused  argentic  fluoride.  A  solution  of  fluoride  of  copper 
in  pure  dilute  hydrofluoric  acid,  with  copper  electrodes, 
conducted  well,  and  yielded  a  good  deposit  of  copper,  with 
a  current  from  a  single  Smee's  cell.  Fluoride  of  copper  is 
insoluble  in  anhydrous  hydrofluoric  acid,  but  dissolves 
quickly  in  aqueous  ammonia. 

If  a  feeble  current  be  passed  by  means  of  copper  elec- 
trodes, through  a  solution  of  chloride  of  copper  dissolved  in 
dilute  hydrochloric  acid,  the  anode  becomes  covered  with 
snow-white  crystals  of  cupreous  chloride,  and  the  cathode 
receives  a  thick  deposit  of  loose,  spongy  copper  ('  Chemical 
News/  vol.  xxii.  p.  167).  Gladstone  and  Tribe  observed, 
that  if  a  strip  of  platinum  was  connected  with  one  of  copper, 
and  both  were  immersed  in  a  solution  of  cupric  chloride,  the 
platinum  became  covered  with  a  layer  of  insoluble  cupreous 
chloride,  also,  that  if  such  a  solution  was  electrolysed  by  a 
feeble  current  with  platinum  electrodes,  chlorine  appeared 
at  the  anode,  and  cupreous  chloride  at  the  cathode ;  but  if 
the  current  was  strong,  metallic  copper  was  also  deposited 
upon  the  edges  of  the  cathode.  Smee  states,  that  a  solution 
of  cupric  chloride  is  less  readily  decomposed  by  an  elec- 
tric current  than  the  nitrate,  but  more  readily  than  the 
sulphate,  and  that  it  is  one  of  the  worst  liquids  for  the  re- 
duction of  copper,  and  the  metal  is  apt  to  assume  a  very 
peculiar  appearance.  He  also  states,  that  the  ammoniuret, 
acetate,  and  hyposulphite,  offer  no  advantages  ;  that  they  are 
difficult  to  decompose,  and  require  a  current  from  several  cells; 
also  the  ammonio-chloride  is  a  bad  solution,  having  a  ten- 
dency to  evolve  hydrogen,  and  yield  a  spongy  copper  deposit ; 
that  iodide  of  copper,  dissolved  in  a  solution  of  iodide  of  po- 
tassium, cannot  be  employed,  because  it  liberates  iodine  ;  that 
a  copper  anode  is  but  little  corroded  in  a  solution  of  sulpho- 
cyanide  of  potassium,  and  the  liquid  does  not  contain  much 
metal ;  and  the  anode  is  very  slightly  acted  upon  in  a  solu- 
tion of  the  potassio-tartrate.  (Compare  Eisner's  statement, 
p.  209.) 


2O2  The  Art  of  Electro-Metallurgy. 

Applications  of  electro-deposition  of  copper. — The  purposes 
to  which  the  electro-deposition  of  copper  has  been  applied, 
are  much  more  numerous  than  those  of  any  other  metal.  It 
is  sometimes  used  for  protecting  iron  and  steel  from  oxida- 
tion, also  to  form  a  basis  for  silvering  and  gilding  upon  zinc, 
iron,  steel,  tin,  lead,  Britannia-metal,  &c. ;  to  the  production 
of  medallions,  busts,  and  even  colossal  statues,  and  many 
other  works  of  art ;  to  the  refining  of  crude  copper  on  the 
large  scale,  the  separation  of  the  metal  from  cupriferous 
solutions  ;  to  making  copies  of  engraved,  stereotype,  and 
daguerreotype  plates  ;  to  the  coating  of  leaves,  flowers,  fruits, 
insects,  &c.,  with  copper,  for  the  purpose  of  ornamentation  ; 
to  the  arts  of  glyphography,  galvanography,  and  electro-tint 
printing;  corrosion  of  the  anode  by  electrolysis,  has  also 
been  applied  in  voltaic  etching.  Bank-notes;  postage 
stamps ;  playing  cards ;  maps  of  the  Ordnance  Survey  ;  and 
the  illustrated  papers  in  which  grocers  and  others  wrap  their 
goods,  are  printed  from  electrotype  copper  plates. 

Coating  articles  with  copper  by  simple  immersion  process. — 
A  vast  number  of  articles  of  a  common  kind,  to  which  it 
is  desired  to  impart  merely  the  appearance  of  copper,  such 
as  steel  pens,  iron  and  steel  wire,  &c.,  are  coated  with  a  film 
of  copper,  by  simply  immersing  them  in  an  acidulated  and 
dilute  solution  of  the  sulphate,  washing  them  thoroughly,  and 
drying  them  quickly  by  rubbing  them  with  hot  sawdust.  To 
effect  this  object,  mix  together  one  measure  of  hydrochloric 
acid,  three  of  water,  and  a  few  drops  of  a  solution  of  sul- 
phate of  copper ;  clean  and  immerse  the  iron,  wash  it,  rub 
it  with  the  cupreous  liquid,  and  re-immerse  it  repeatedly, 
adding  a  few  drops  of  the  copper  solution  occasionally. 

According  to  O.  Gaudain,  articles  of  cast-iron,  wrought 
iron,  and  steel,  may  be  coated  with  copper,  by  dipping  them 
into  a  melted  mixture  of  chloride  and  fluoride  of  copper,  with 
five  or  six  parts  of  cryolite,  and  a  little  chloride  of  barium, 
contained  in  a  plumbago  crucible  ('Journal  of  the  Chemi- 
cal Society,'  vol.  xi.  p.  955).  To  coat  brass  with  copper, 


Separation  of  Copper  from  Ctipriferous  Liquids.  203 

Dr.  C.  Puscher  directs  us  to  dissolve  ten  parts  of  sulphate  of 
copper,  and  five  of  salammoniac,  in  150  of  water.  Immerse 
the  previously  cleaned  articles  in  this  liquid  for  one  minute, 
drain  them,  and  then  heat  them  over  a  charcoal  fire  until 
the  ammoniacal  salt  is  expelled,  and  the  coating  of  copper 
appears  perfect,  then  wash  them  with  water,  and  dry  them 
('  Chemical  News,'  vol.  xxiii.  p.  215). 

M.  Weis  Kopp,  deposits  copper  upon  cast  iron,  by 
the  simple  immersion  process,  in  a  bath  composed  of  ten 
parts  of  nitric  acid,  ten  of  chloride  of  copper,  and  eighty  of 
hydrochloric  acid  of  specific  gravity  1*105.  He  immerses 
them  several  times,  until  a  sufficient  deposit  is  obtained, 
rubbing  them  with  a  woollen  cloth  between  each  immer- 
sion. The  articles  are  first  cleaned  in  a  mixture  of  one 
part  of  nitric  acid,  and  fifty  of  hydrochloric  acid  of  specific 
gravity  1*105  ('Chemical  News,'  vol.  xxi.  p.  47).  For 
coating  iron  wire  with  a  film  of  copper  by  this  method, 
Roseleur  uses  a  mixture,  composed  of  fifty  to  a  hundred 
parts  of  water,  one  of  sulphate  of  copper,  and  one  of 
sulphuric  acid ;  and,  if  the  deposit  is  not  sufficiently  adhe- 
rent, the  copper  is  compressed  by  drawing  the  wire  through 
a  hole  in  a  steel  plate.  He  coats  small  articles,  by  burying 
them  in  sawdust  wetted  with  this  solution,  diluted  with  three 
or  four  times  its  volume  of  water,  and  tossing  the  articles  and 
sawdust  about. 

Separation  of  copper  from  cupriferous  liquids. — Extremely 
large  deposits  of  sulphide  of  iron,  containing  a  greater  or 
less  percentage  of  cupric  sulphide,  exist  in  mineral  strata. 
These  sulphides,  by  exposure  to  air  and  water,  become 
more  or  less  oxidised  into  sulphates,  and  are  rendered 
soluble.  In  this  way,  the  water  of  certain  mines  becomes 
impregnated  with  sulphate  of  copper,  and  from  very 
ancient  times,  copper  has  been  separated  in  the  metallic 
state  from  such  waters,  by  immersing  fragments  of  iron 
in  them.  Of  late  years,  these  immense  deposits,  (notably 
those  of  the  Tharsis  and  Rio  Tinto  mines  in  Spain,)  have 


2O4  The  A  rt  of  Electro- Metallurgy. 

been  worked  by  scientific  processes,  and  all  their  constituents 
utilised.  The  sulphur  contained  in  them  is  burned  and  con- 
verted into  oil  of  vitriol,  and  has  become  one  of  the  chief 
sources  of  supply  of  that  acid.  The  sulphide  of  iron,  con- 
verted into  oxide  by  that  process,  is  next  mixed  with  common 
salt,  and  the  mixture  roasted,  to  render  the  copper  soluble,  a 
quantity  of  hydrochloric  acid  being  at  the  same  time  produced 
from  the  common  salt,  and  collected.  By  washing  the  roasted 
mixture  with  the  dilute  hydrochloric  acid,  and  with  water, 
all  the  copper  is  extracted  as  a  greenish-blue  liquid.  This 
liquid  is  run  into  large  vats  filled  with  scraps  of  iron,  and 
kept  hot  by  passing  steam  into  it.  In  a  short  time  all  the 
copper  is  reduced  in  the  form  of  feathery  crystals  upon 
the  iron,  and  falls  to  the  bottom  of  the  liquid  as  a  red 
powder ;  which  is  separated  from  the  iron,  and  refined 
in  the  usual  manner.  The  washed  oxide  of  iron  is 
employed  as  a  source  of  metallic  iron,  and  for  '  fettling ' 
furnaces.  In  this  way,  great  quantities  of  copper  are 
yearly  obtained,  and  many  hundreds  of  thousands  of  tons 
of  a  substance,  for  which  there  previously  existed  no  uses, 
are  beneficially  utilised.  The  process  usually  employed,  is 
the  one  patented  by  Mr.  Henderson. 

Deposition  of  copper  by  contact  with  another  metal  (see 
also  p.  82). — The  electro-deposition  of  copper  upon  cast- 
iron  fountains,  lamp  posts,  &c.  is  very  common  in  fans. 
The  process  of  M.  Fred  Wiels,  is  as  follows : — Dissolve 
in  1,000  parts  of  water,  150  of  sodio-potassic  tartrate, 
eighty  of  soda-lime  containing  from  50  to  60  per  cent 
of  free  soda,  and  thirty-five  of  sulphate  of  copper.  Iron 
and  steel,  and  the  metals  whose  oxides  are  insoluble  in 
alkalies,  are  not  corroded  in  this  solution.  The  iron  or 
steel  articles,  are  cleaned  with  dilute  sulphuric  acid,  of 
specific  gravity  1*014,  by  immersing  them  in  that  liquid 
from  five  to  twenty  minutes,  then  washed  with  water,  and 
finally  with  water  made  alkaline  by  soda,  then  cleaned  with 
the  scratch-brush,  again  washed,  and  then  immersed  in  the 


Coppering  Cast-iron  Cylinders.  205 

cupreous  bath,  in  contact  with  apiece  of  zinc  or  lead,  or  sus- 
pended by  means  of  zinc  wires ;  the  latter  is  the  most  economi- 
cal way.  The  articles  must  not  be  in  contact  with  each  other. 
They  thus  receive  a  strongly-adherent  coating  of  copper, 
which  increases  in  thickness  (within  certain  limits)  with  the 
duration  of  immersion.  Pure  tin  does  not  become  cop- 
pered, by  contact  v/ith  zinc  in  this  solution* ;  it  oxidises,  and 
its  oxide  decomposes  the  solution,  and  precipitates  red  sub- 
oxide  of  copper,  and  by  prolonged  action,  all  the  copper  is 
thus  removed  from  the  liquid.  The  iron  articles  require  to 
be  immersed  from  three  to  seventy-two  hours  according  to 
the  colour,  quality,  and  thickness  of  the  required  deposit. 
The  copper  solution  is  then  run  out  of  the  vat,  and  the 
coated  articles  washed  in  water,  then  cleaned  with  a 
scratch-brush,  washed,  dried  in  hot  saw-dust,  and  then  in  a 
stove.  To  keep  the  bath  of  uniform  strength,  the  liquid  is  re- 
newed from  below,  and  flows  away  in  a  small  stream  at  the 
top.  After  much  use,  the  exhausted  liquid  is  renewed,  by 
precipitating  the  zinc  by  means  of  sulphide  of  sodium, 
(not  in  excess),  and  re-charging  the  solution  with  cupric 
sulphate.  He  also  supplies  to  the  bath,  hydrated  oxide  of 
copper  ('  Chemical  News/  vol.  xiii.  p.  i). 

By  simple  cell  process.  Coppering  cast-iron  cylinders  for 
calico  printing. — M.  Schlumberger's  process.  The  cylinder 
(having  been  perfectly  cleaned  by  the  usual  methods,)  is  made 
the  cathode  (with  a  current  from  four  or  six  elements)  during 
twenty-four  hours,  in  a  mixture  of  two  liquids,  composed  of 


Parts 

Water       .         .         .         .12 
Cyanide  of  potassium          .       3 


Parts 

Water  .     16 

Sodic  carbonate          .         .       4 
,,     sulphate  ...       2 
Cupric       ,,  .         .1 

It  is  then  well  washed,  rubbed  with  pumice  powder,  then 
washed  again  with  an  aqueous  solution  of  cupric  sulphate, 
of  specific  gravity  1*161,  containing  ^J-^  part  of  its  volume 
of  sulphuric  acid,  scraps  of  copper  being  kept  in  the  bath 


206  The  A  rt  of  Electro-Metallurgy. 

to  supply  the  loss  of  copper,  and  prevent  the  liquid  becoming 
too  acid.  It  is  immersed  again  in  the  above  alkaline  solu- 
tion, or  else  in  a  mixture  composed  of  two  liquids,  viz.  : — 


Parts 

Water  .  .  .  .10 
Cyanide  of  potassium  .  3 
Aqueous  ammonia  •  .3 


Parts 
Water  .     16 

Sodic  carbonate         .         .       4 
„     sulphate  ...       2 


Cupric  acetate  ...       2 

In  these  mixtures,  at  a  temperature  of  15°  to  18°  C,  it  is  sur- 
rounded by  porous  cells  containing  zinc  rods  and  dilute  sul- 
phuric acid,  and  connected  with  the  zinc  by  copper  wires. 
The  cylinders  are  turned  partly  round  once  a  day,  in  order 
to  render  the  deposit  uniform,  and  the  action  is  continued 
during  three  to  four  weeks,  until  the  deposit  is  ^gth  of  an 
inch  thick  (G.  Schaeffer,  '  Chemical  News,'  vol.  xxx.  p.  219  ; 
'Journal  of  the  Chemical  Society,'  vol.  xiii.  p.  I96).1 

Deposition  of  copper  by  separate  current  process. — In  de- 
positing copper  by  the  single  cell  method,  a  nearly  saturated 
solution  of  sulphate  of  copper  answers  very  well,  but  for 
the  battery  process,  an  excellent  solution  may  be  made,  by 
dissolving  four  parts,  by  weight,  of  finely  powdered  sulphate 
of  copper  (best  quality),  and  one  of  sulphuric  acid,  in 
about  eighteen  or  twenty  of  water,  and  then  filtering 
it ;  neither  of  these  solutions  however,  are  fit  to  deposit 
copper  upon  steel,  iron,  or  zinc,  because  the  electrical  rela- 
tions are  unsuitable  ;  these  metals  decompose  such  liquids 
rapidly,  and  deposit  the  copper  upon  themselves  by  simple 
immersion.  Some  persons  use  a  solution  containing  a 
smaller  proportion  of  acid,  a  greater  one  of  copper  salt,  and 
less  water ;  and  others  add  a  small  quantity  of  sulphate  of  zinc 
or  sulphate  of  potassium  to  the  liquid ;  the  latter  is  very  good. 

Deposition  of  copper  upon  metals. — The  sulphate  solu- 
tion is  used  for  coating  all  metals  and  alloys,  such  as 
brass  and  german-silver,  which  do  not  decompose  that 
liquid  ;  but  zinc,  iron,  steel,  tin,  lead,  Britannia-metal,  type- 

1  See  also  H.  Wildes,  patent  No.  4515,  Dec.  28,  1875. 


Coppering  Base  Metals.  207 

metal,  &c.,  which  precipitate  the  copper  from  such  a  liquid 
by  simple  immersion,  are  coated  in  the  cyanide  or  other 
alkaline  solution ;  and  as  the  deposition  of  copper  from  an 
alkaline  liquid  is  more  expensive  than  that  from  the  sulphate, 
if  a  greater  thickness  of  metal  is  required,  the  additional 
thickness  is  put  on  the  articles  in  the  sulphate  solution. 

Deposition  of  copper  upon  zinc,  iron,  &>c. — Various  solu- 
tions are  employed  for  this  purpose,  but  they  are  all  alkaline 
ones,  and  mostly  contain  cyanide  of  copper  dissolved  in 
cyanide  of  potassium.  A  very  good  one  may  be  formed 
thus  : — Dissolve  cyanide  of  copper  to  saturation  in  water 
containing  about  two  pounds  of  cyanide  of  potassium  to 
the  gallon,  and  then  add  about  four  ounces  more  of  the 
potassic  salt  per  gallon,  to  form  free  cyanide  ;  the  liquid  is 
then  ready,  and  should  be  used  at  a  temperature  of  about 
150°  Fahr.  Cyanide  of  copper  is  not  very  soluble  in  cyanide 
of  potassium  solution,  the  liquid  formed,  does  not  readily 
dissolve  the  anode,  nor  does  it  conduct  well ;  it  also  has  a 
strong  tendency  to  evolve  hydrogen  at  the  cathode,  but  this 
may  be  lessened,  or  wholly  prevented,  by  avoiding  the  use  of 
any  free  cyanide  of  potassium,  employing  a  weaker  current, 
and  adding  some  aqueous  ammonia  and  oxide  of  copper. 

Watt  recommends  a  solution,  composed  of  one  gallon 
of  water,  six  ounces  of  cyanide  of  potassium,  four  of 
carbonate  of  potassium,  two  of  liquid  ammonia,  and  two 
of  cupric  sulphate.  Dissolve  the  sulphate  of  copper 
in  rain  water,  and,  when  cold,  add  the  carbonate 
of  potassium,  and  the  ammonia.  When  the  precipi- 
tate is  re-dissolved,  add  the  cyanide.  Decant  the  clear 
liquid  for  use.  Another,  recommended  by  Roseleur,  is, 
to  reduce  twenty  parts  of  crystallised  cupric  acetate  to 
powder,  and  rub  it  to  a  paste  with  a  little  water,  add  to  it 
200  parts  of  water  containing  twenty  parts  of  dissolved 
washing-soda,  and  stir  the  mixture  ;  a  light  green  precipitate 
is  formed  ;  twenty  parts  of  bisulphite  of  sodium  are  now  dis- 
solved in  200  parts  of  water,  and  the  solution  mixed  with 


208  The  A  rt  of  Electro-Metallurgy. 

the  former  one  ;  the  precipitate  becomes  dirty  yellow.  And, 
lastly,  dissolve  twenty  parts  of  perfectly  pure  cyanide  of 
potassium,  in  600  of  water,  and  add  it  to  the  previous 
mixture.  If  the  solution  is  not  quite  colourless,  add  more 
cyanide  until  it  is  so.  This  liquid  may  be  used  either  hot 
or  cold,  and  requires  a  current  of  moderate  strength.  An- 
other very  good  liquid,  which  may  be  employed  either  hot  or 
cold,  consists  of  2,500  parts  of  water,  fifty  of  potassic 
cyanide  of  70  per  cent.,  thirty- five  of  acetate  of  copper, 
thirty  of  bisulphite  of  sodium,  and  twenty  of  aqueous 
ammonia.  The  cyanide  and  bisulphite,  are  to  be  dissolved 
in  one  part  of  the  water,  and  the  ammonia  and  acetate  of 
copper  in  the  other,  and  the  two  solutions  mixed  together. 
If  the  blue  solution  of  acetate  of  copper  in  aqueous  ammo- 
nia, does  not  then  become  quite  colourless,  a  little  more 
cyanide  must  be  added.  If  these  liquids  are  used  hot,  the 
deposition  is  more  rapid.  If  they  become  green,  or  blue,  by 
working,  it  is  from  an  excess  of  copper  dissolved,  and  either 
the  anode  should  be  reduced  in  size,  or  some  cyanide  of 
potassium  added.  And  if  the  anode  acquires  a  brown  or 
white  insoluble  coating,  the  liquid  is  deficient  in  copper,  and 
some  of  the  solution  of  acetate  of  copper  in  ammonia,  must 
be  added. 

A  good  depositing  solution,  for  coating  iron  and  steel  by 
the  battery  process,  may  be  made,  by  dissolving  ammoniuret 
of  copper  in  a  solution  of  cyanide  of  potassium.  Nine 
hundred  or  1,000  parts  of  water,  containing  eighty  parts 
of  cyanide  of  potassium,  dissolve  forty  parts  of  the  blue 
ammoniuret,  and  form  a  colourless  liquid. 

W.  H.  Walenn's  solution  for  coppering  iron,  consists  of 
cyanide  of  copper  dissolved  to  saturation,  in  a  solution  of 
equal  parts  of  potassic  cyanide,  and  ammonium  tartrate,  and 
sufficient  oxide  of  copper,  and  ammoniuret  of  copper  added, 
to  prevent  evolution  of  hydrogen  at  the  surface  of  the  arti- 
cles. The  solution  is  used  at  80°  C.  (=176°  Fahr.).  In 
this  process,  one  Smee's  cell  may  be  employed.  The  cost 


Management  of  Copper  Solutions.  209 

has  been  found  to  be  about  2s.  6d.  per  pound  of  metal  depo- 
sited. One  ounce  and  a  half  of  copper  per  square  foot  will 
protect  iron  from  rust  ('  Chemical  News,'  vol.  xxi.  p.  247 ; 
vol.  xxii.  p.  181). 

Dr.  Eisner  coats  base  metals  with  copper,  in  a  solution 
made  as  follows  : — One  part  of  bitartrate  of  potassium  in 
powder,  is  boiled  in  ten  parts  of  water,  and  as  much  freshly 
prepared,  and  wet  hydrated  carbonate  of  copper  (which  has 
been  washed  with  cold  water),  stirred  with  it,  as  the  liquid 
will  dissolve.  The  beautiful  dark  blue  alkaline  liquid  is  fil- 
tered, and  rendered  still  more  alkaline  by  addition  of  a 
small  quantity  of  carbonate  of  potassium.  A  copper  anode 
dissolves  readily  in  the  liquid  (compare  Smee's  statement, 
p.  201),  and  the  solution  may  be  employed  to  coat  objects 
composed  of  tin,  cast  iron,  and  zinc  ('  Chemist/  vol.  vii. 
p.  124). 

Management  of  copper  depositing  liquids. — Sulphate  of 
copper  depositing  solutions  are  the  most  easy  of  any  to 
manage,  because  the  range  within  which  the  density  of  the 
current  may  be  varied,  without  causing  a  bad  deposit,  is 
greater  than  with  those  of  any  other  metal,  not  even  except- 
ing antimony  ;  much  however,  depends  with  copper,  as 
with  other  metals,  upon  the  kind  of  liquid  employed  ;  many 
cupreous  solutions  are  difficult  to  manage,  and  none  are 
as  easy  as  the  sulphate  ;  the  alkaline  ones,  employed  for 
coppering  iron,  etc.,  are  much  more  difficult  to  obtain  a 
thick  deposit  from,  than  the  sulphate. 

The  general  rules  which  determine  and  regulate  the  quality 
of  other  deposited  metals,  operate  also  with  copper ;  if  the 
current  is  too  great  in  relation  to  the  amount  of  receiving 
surface,  the  metal  is  set  free  as  a  brown  or  nearly  black 
metallic  powder,  and  hydrogen  gas  may  even  be  deposited 
with  it  and  evolved.  In  the  sulphate  solution,  if  the  liquid 
is  too  dense,  streaks  are  apt  to  be  formed  upon  the  receiving 
surface,  and  the  article  (especially  if  a  tall  one)  will  receive 
a  thick  deposit  at  its  lower  part,  and  a  thin  one  at  the 

p 


2 1  o  The  A  rt  of  Electro-Metallurgy. 

upper  portion,  or  even  have  the  deposit  on  the  upper  end 
re-dissolved.  If  there  is  too  little  water,  crystals  of  sulphate 
of  copper  form  upon  the  anode,  and  sometimes  even  upon 
the  cathode,  at  its  lower  part,  and  also  at  the  bottom  of 
the  vessel.  If  there  is  too  much  acid,  the  anode  is  cor- 
roded whilst  the  current  is  not  passing.  The  presence  of  a 
trace  of  bisulphide  of  carbon  in  the  sulphate  solution  will 
make  the  deposit  brittle,  and  this  continues  for  some  time, 
although  the  solution  is  continually  depositing  copper  ;  in 
the  presence  of  this  substance,  the  anode  becomes  black,  but 
:f  there  is  also  a  great  excess  of  acid,  it  becomes  extremely 
bright.  Solutions  of  cupric  sulphate,  containing  sulphate  of 
potassium,  and  the  bisulphide  of  carbon  applied  to  them, 
are  sometimes  employed  for  depositing  copper  in  a  bright 
condition.  The  copper  obtained  from  the  usual  double 
cyanide  of  copper  and  potassium  solution,  by  a  weak  current, 
is  of  a  dull  aspect,  but  with  a  strong  current  it  is  bright. 

Rapidity  and  cost  of  depositing  copper. — If  a  good  sul- 
phate solution,  and  a  strong  current  are  employed,  a  thick- 
ness of  \  of  an  inch  of  firm  copper  can  be  deposited,  either 
by  the  single  cell,  or  the  separate  current  process,  in  about 
seven  to  ten  days.  The  cost  of  copper  deposited  by  a 
current  from  a  battery,  is  usually  estimated  at  2s.  or  2s.  6d. 
per  pound,  but  upon  the  large  scale,  by  means  of  currents 
from  magneto-electric  machines  driven  by  steam  power,  ob- 
tained under  the  most  economical  circumstances —as,  for  in- 
stance, by  waste  heat  from  other  processes — it  is  probably 
less  than  2d.  per  pound,  exclusive  of  the  value  of  the  metal. 

Composition  of  the  dirt  upon  copper  anodes. — Everyone 
who  has  deposited  copper  from  the  sulphate  by  electrolysis, 
has  observed  how  black  and  dirty  the  anodes  become,  be- 
cause he  has  been  obliged  to  frequently  wash  them.  Max, 
Duke  of  Leuchtenberg,  analysed  this  black  matter  and  found 
in  it — 


A  nalysis  of  Dirt  from  A  nodes. 

Tin     ........  33-50 

Oxygen        ......         .  24*82 

Copper        .......  9-24 

Antimony    .         .         .         ...         .  9*22 

Arsenic       .         .         .         .         .         .         .  7-20 

Silver           .         ......  4-45 

Sulphur       .....         .  2*46 

Nickel         .         .         .         .         .                  .  2-26 

Silica  .         .         .         .         .  .       .  .       .1-90 

Selenium     .         .         .         .         .         ...  1*27 

Gold  .         .         .  ,       .         .         .         .         .  -98 

Cobalt         .......  -86 

Vanadium  ......         .  '64 

Platinum     .......  '44 

Iron    ........  '30 

Lead  ........  -15 


2  r  I 


(See  Erdmann's  <  Journal  of  Practical  Chemistry/  vol. 
xlv.,  1848,  pp.  460-468.) 

The  following  analyses  of  similar  residues  have  been 
kindly  supplied  to  me  by  a  friend  :  — 


No.  I, 


No.  II. 


Copper         .         .         . 

85-850 

Lead   . 

Water  and  oxygen 

4-950 

Water  and  oxygen 

Arsenic         .         .         . 

2-480 

Copper 

Silver  . 

1-815 

Antimony     . 

Sulphuric  acid 

1-150 

Sulphur 

Insoluble  earthy  matter 

0-950 

Silver  .         , 

Antimony     .         .         . 

750 

Arsenic 

Iron               , 

750 

Earthy  matter       . 

Bismuth 

•650 

Bismuth        .         , 

Alumina 

•250 

Chlorine       .     '    . 

Chlorine 

•250 

Iron     .         . 

Gold    . 

•085 

Nickel 

Lead    . 

•050 

Organic  matter 

Loss    . 

•020 

Gold    . 

100  '000 

Loss     .         . 

Per  ton  of  20  cwt. 

ozs.  dwts.  grs. 

Per  ton  of  20  cwt. 

Silver  =  623     2     8 

Silver  =1835  ozs. 

Gold  =   27  15     8 

Gold  =       3  ozs. 

P  2 


2 1 2  The  A  rt  of  Electro-Metalhirgy. 

No.  III. 

Copper      .         .        .         .        .         .         .67-90 

Sulphur 18-10 

Iron.         . 5-55 

Insoluble  earthy  matter       ....  3  -40 

Organic  matter  .         .         .         .         .         .  2-25 

Lead          . 2-05 

Silver        .         .         .         .  0-55 

Loss           .  •       .  •       .         .         .         .         .  -20 

lOO'OO 

Refining  crude  copper  by  means  of  electrolysis. — The  fore- 
going analyses  throw  great  light  upon  the  question,  why  it 
is,  that  electro-deposited  copper  (and  also  that  found  in  the 
metallic  state  in  fissures  in  rocks  at  Lake  Superior,  and  other 
places,1)  is  so  very  pure ;  and  also  upon  the  process  of  re- 
fining crude  copper  by  electrolysis.  Several  hundreds  of 
tons  of  copper,  are  yearly  refined  by  Mr.  James  Elkington's 
patent  process  ('  Chemical  News,'  vol.  xxi.  p.  264).  This 
simply  consists  in  making  large  slabs  of  the  crude  metal  (ob- 
tained from  the  ores  by  the  usual  melting  process),  the  anodes 
in  the  ordinary  sulphate  of  copper  depositing  liquid,  and 
passing  electric  currents  from  numerous  magneto-electric 
machines  through  them  and  the  liquid ;  a  '  compound  depo- 
siting vessel '  (see  pp.  24,  90)  and  a  series  of  electrodes 
being  employed.  The  ropper  dissolves,  and  nearly  all  the 
impurities  are  separated,  and  fall  to  the  bottom  as  a  dirty 
powder.  The  impurities  vary  of  course,  with  the  composition 
of  the  crude  metal,  and  the  success  of  the  process  depends 
largely,  upon  the  selection  of  such  crude  metal  as  contains 
no  such  substances,  as  would  be  electro-deposited  along  with 
the  copper.- 

In  this  process,  the  metalloids,  such  as  oxygen,  sul- 
phur, selenium,  phosphorus  (and  perhaps  arsenic),  carbon, 

1  A  mass  of  copper,  estimated  to  weigh  between  75  and  100  tons, 
was  discovered  at  Eagle  Harbour,  Lake  Superior. 


Refining  Copper  by  Electrolysis.  2 1 3 

boron,  and  silicon,  are  not  liberated  at  the  cathode.  Any 
silver  present,  will  not  dissolve,  because  the  sulphuric  acid 
employed,  contains  a  little  hydrochloric  acid,  which  converts 
it  into  insoluble  chloride.  Gold,  if  traces  of  it  are  present, 
is  also  insoluble.  Lead  is  converted  into  sulphate,  which  is 
its  most  insoluble  compound,  and  the  small  portion  which 
does  dissolve,  is  not  deposited,  because  lead  is  electro-posi- 
tive to  copper,  and  therefore  copper  is  deposited  first. 
Carbon,  together  with  any  sulphides  present,  also  falls  to  the 
bottom  as  an  insoluble  powder.  Iron  dissolves,  but  being 
highly  electro-positive  to  copper  in  such  a  liquid,  is  not 
deposited,  even  when  present  in  very  great  amount.  Zinc 
is  probably  not  present,  but,  if  it  is,  behaves  like  iron,  and  is 
more  highly  electro-positive.  Tin  is  probably  not  dissolved, 
and  if  it  were,  being  positive  to  copper,  would  not  be  de- 
posited. Cobalt  behaves  like  iron,  but  the  quantity  present 
is  very  minute.  Nickel  dissolves,  and  if  in  very  large 
quantity,  would  be  deposited  to  a  small  extent  along  with 
the  copper,  but  its  proportion  is  also  very  small.  Antimony 
(and  perhaps  also  arsenic  to  a  less  extent)  would  be  the  most 
likely  metal  to  contaminate  the  deposit. 

Analytical  estimation  of  copper  in  alloys  and  ores  by  means 
of  electrolysis. — In  consequence  of  the  possibility,  by  attend- 
ing to  proper  precautions,  of  depositing  copper  alone  from 
a  solution  of  its  sulphate  containing  other  metals,  attempts 
have  been  made  to  separate  the  whole  of  the  copper  from 
those  metals  by  such  a  process,  and  thus  determine  its 
amount,  and  a  premium  of  300  thalers,  or  457.,  was  offered 
by  the  directors  of  the  Mansfield  copper  mines,  in  Germany, 
for  a  satisfactory  method.  The  successful  competitor  was 
Mr.  C.  Luckow,  chief  chemist  to  the  Cologne- Minden  Rail- 
way Company.  The  process  is  extensively  used,  and  a  full 
description  of  it  may  be  found  in  the  '  Chemical  News/  vol. 
xix.,  1869,  p.  221.  (See  also  Watts's  '  Chemical  Dictionary' 
2nd  supplement,  p.  384.)  J.  M.  Merrick  has  also  electro- 
lysed known  weights  of  pure  sulphate  of  copper  in  aqueous 


214  The  Art  of  Electro- Metallurgy. 

solution,  in  a  covered  platinum  crucible,  with  a  platinum 
wire  for  the  anode,  and  the  crucible  for  the  cathode,  with  a 
current  from  two  or  three  Grove's  cells,  until  all  the  metal 
was  deposited,  and  then  weighed  the  deposits.  In  two  experi- 
ments, the  percentages  of  copper  obtained,  were  25-44,  and 
25*46,  theory  requiring  25-46  per  cent.  The  deposits  were 
washed  with  alcohol  and  cautiously  dried  ('  Chemical  News,' 
vol.  xxiv.  pp.  100-172). 

Preventing  adhesion  of  deposit. — In  all  cases  where  a  per- 
fect copy  is  required  of  a  metal  plate,  or  other  metallic  ob- 
ject, the  surface  to  receive  the  deposit,  must  be  sufficiently 
clean  to  enable  the  electricity  to  freely  enter,  but  not  so  per- 
fectly unstained  as  to  cause  the  deposit  to  adhere  so  firmly 
that  it  cannot  be  separated.  To  prevent  adhesion,  the  metal, 
after  having  been  cleaned  and  dried,  should  remain  exposed 
some  time  to  the  air  before  being  put  into  the  depositing 
liquid  ;  it  should  also  not  be  heated  immediately  before  im- 
mersion ;  and  if  a  wire  has  to  be  soldered  to  it,  that  should 
be  done  beforehand.  It  should  also  not  be  put  into  the 
solution  without  first  making  all  the  connections  of  the  cir- 
cuit complete,  and  attaching  it  to  the  battery,  otherwise 
the  momentary  immersion  may  corrode  and  clean  its  surface. 
To  make  perfectly  certain  of  preventing  adhesion,  without 
preventing  a  deposit,  the  dry  surface  of  the  metal  may  be 
brushed  with  a  thick  camel-hair  brush  with  short  hairs,  and 
some  fine  black-lead,  before  immersion,  in  addition  to  taking 
the  above  precautions.  In  some  cases,  the  articles  to  be 
copied,  are  rubbed  with  cotton-wool  slightly  moistened  with 
a  very  weak  solution  of  beeswax,  prepared  by  dissolving  a 
fragment  of  wax  of  the  size  of  a  pea  in  a  quarter  of  a  pint 
of  spirit  of  wine.  In  other  cases  they  are  rubbed  over  with 
a  little  olive-oil,  and  then  wiped  as  clean  as  possible  by 
rubbing  with  cotton-wool.  To  prevent  adhesion  of  de- 
posits on  copper,  or  on  steel,  vapour  of  iodine  is  also 
employed. 

Copying  engraved  copper-plates,    medallions,    &c. — En- 


Preventing  A  dJiesion  of  Deposits.  2 1 5 

graved  steel  plates,  are  copied  by  coating  ('  stopping  off ')  the 
back  and  edges  with  copal  varnish,  allowing  the  varnish  to 
become  perfectly  dry ;  immersing  the  plate  in  the  cyanide 
coppering  liquid,  and  depositing  a  thin  film  of  metal  upon 
it,  then  washing  it  well,  and  at  once  suspending  it  in  the 
sulphate  of  copper  solution,  and  depositing  the  desired  thick- 
ness ;  this  will  require  from  twenty-four  to  forty-eight  hours. 
The  surface  of  the  steel  should  be  previously  prepared  for 
a  non -adhesive  deposit,  otherwise  the  two  metals  cannot  be 
separated.  If  the  plate  to  be  copied,  is  a  copper,  brass, 
silver,  or  gold  one,  it  rn^y  receive  the  entire  deposit  in  the 
sulphate  solution.  Medallions  and  other  forms  of  metal, 
may  also  be  copied  in  a  similar  manner.  As  the  metal  in 
all  such  cases,  has  a  great  tendency  to  be  deposited  upon 
the  edges,  the  deposit  creeps  round  those  parts,  and  this 
superfluous  copper  has  to  be  filed  off  before  the  two  can  be 
separated.  When  they  are  taken  apart,  their  surfaces  are 
found  to  be  perfectly  dry. 

Copying  Daguerreotype  pictures  in  copper. — First  sclder  a 
wire  to  the  back  of  the  plate  near  the  edge ;  varnish  the  back 
and  edges,  and  allow  it  to  dry ;  hang  it  (taking  the  above 
precautions)  in  a  clean  sulphate  of  copper  solution,  which  is 
perfectly  free  from  dust  or  grease  on  its  surface,  and  in  the 
course  of  twenty  or  thirty  hours  (if  about  two  pairs  of  Smee's 
batteries  have  been  used),  the  deposit  will  be  sufficiently  thick 
to  be  removed  ;  it  should  then  be  taken  out,  well  washed, 
wiped  perfectly  dry,  and  a  narrow  strip  cut  off  its  edges 
with  a  strong  pair  of  scissors  or  shears  ;  the  two  may  then 
be  easily  separated  by  inserting  the  blade  of  a  knife,  or  the 
end  of  a  thin  wedge  of  hard  wood,  between  them  at  the 
edges.  If  the  process  has  been  carefully  managed,  and  the 
original  picture  is  a  strong  one,  a  most  beautiful  and  vivid 
copy  will  be  obtained ;  and  if  the  picture  is  not  only  a 
strong  one,  but  has  been  fixed  by  Fizeau's  process,  a  number 
of  successive  copies  may  be  taken  from  it,  but  their  inten- 
sity, as  well  as  that  of  the  original,  diminishes  in  each  sue- 


2 1 6  The  A  rt  of  Electro-Metallurgy. 

ceeding  trial.  With  a  vivid  original  picture,  clear  solution, 
very  regular  and  undisturbed  action  of  the  battery,  and  a 
fine  deposit,  there  may  be  observed  a  most  strange  pheno- 
menon; it  will  be  found  that  the  picture  has  not  entirely 
disappeared,  even  in  twenty  hours,  although  the  coating  of 
copper  has  constantly  increased  in  thickness ;  the  image  has 
penetrated  quite  through  the  deposited  metal,  and  appeared 
upon  the  back,  even  with  deposits  as  thick  as  an  address 
card.  In  some  cases  the  figure  is  optically  positive,  and  in 
others  negative. 

Coppering  cloth. — Mr.  J.  Schottlaender  took  out  a  patent, 
Dec.  8,  1843,  for  depositing  either  plain  or  figured  copper 
upon  felted  fabrics.  He  passes  the  cloth  under  either  a 
plain  or  engraved  copper  roller,  horizontally  immersed  in  a 
sulphate  of  copper  solution,  (not  containing  much  fiee  acid,) 
and  a  deposit  takes  place  upon  the  roller  as  it  slowly  revolves ; 
the  meshes  of  the  cloth  are  thus  filled  with  metal,  and  the 
design  of  the  roller  copied  upon  it;  the  coppered  cloth  is 
slowly  rolled  off,  and  passed  through  a  second  and  closely 
contiguous  vessel  filled  with  clean  water.  The  roller  is  pre- 
viously prepared  for  a  non-adhesive  deposit. 

Deposition  of  copper  upon  non-metallic  surfaces.—  A  suffi- 
ciently large  conducting  wire  of  copper  is  first  attached  to 
the  object,  and,  if  necessary,  a  number  of  'guiding  wires  ' 
formed  of  very  fine  brass  wire,  are  attached  to  the  main  wire, 
and  their  free  ends  stuck  into  the  surface  of  the  article,  in 
those  parts  only  where  deposition  is  the  most  difficult  to 
effect,  such  as  in  recesses  or  deeply  undercut  parts  of 
the  mould,  which  are  the  most  distant  from  the  anode, 
or  into  which  exhausted  portions  of  the  solution,  would 
ascend  and  collect.  All  light  moulds  and  articles,  require 
to  be  weighted,  in  order  to  make  them  sink  in  the  so- 
lution ;  lead  is  usually  employed  for  this  purpose. 

To  deposit  copper  (or  other  metal)  upon  non-conductors, 
their  surfaces  must  be  rendered  conductive.  To  effect  this 
object,  there  are  two  methods  in  use :  first,  to  cover  them  with 


Coppering  Non-Metallic  Surfaces.  2I1? 

a  thin  film  of  black-lead,  or  the  finest  quality  of  metallic 
bronze-powder,  by  brushing ;  or,  second,  to  coat  them  with 
a  minute  film  of  gold  or  stiver,  by  chemical  means.  The 
first  of  these  methods  is  generally  used  for  moulds  com- 
posed of  gutta-percha,  wax,  resinous  composition,  or  plaster 
saturated  with  oil,  where  the  parts  are  not  much  undercut ; 
the  second  for  elastic  moulds,  because  they  will  not  bear 
the  friction  of  black-leading,  and  because  the  black-lead  can- 
not be  readily  applied  to  all  their  recesses. 

In  employing  black-lead,  care  should  be  taken  to  select 
a  kind  which  conducts  electricity  freely  ;  and  this  can  only 
be  found  by  actual  trial.  Some  specimens  conduct  very 
badly,  and  others  very  well.  It  should  be  applied  to  the  sur- 
face, by  persistent  brushing  with  a  camel-hair  brush,  having 
a  large  and  thick  body  of  short  hairs;  breathing  upon  the 
face  of  the  article  occasionally,  to  facilitate  the  adhesion  of 
the  black-lead,  and  when  the  surface  is  perfectly  black  and 
bright,  blowing  off  the  superfluous  powder.  The  whole 
operation  occupies  about  ten  or  fifteen  minutes  with  a  small 
object  the  first  time  of  preparing  it,  but  less  in  subsequent 
operations  with  the  same  surface.  A  small  quantity  of  black- 
lead  is  sufficient  for  a  very  large  surface.  The  conducting 
power  of  black-lead  is  greatly  improved  by  gilding  or  sil- 
vering it.  It  may  be  gilded  as  follows  : — Dissolve  one  part 
of  chloride  of  gold  in  100  parts  of  sulphuric  ether  in  a  bottle, 
add  fifty  parts  of  the  plumbago,  mix  them  thoroughly,  and 
expose  the  mixture  in  the  open  bottle  to  sunlight,  stirring  it 
frequently  until  it  is  perfectly  dry ;  apply  it  by  brushing. 

A  plan  which  I  have  devised,  and  which  is  cheaper  than 
this,  is  to  mix  with  the  black-lead,  one-third  of  its  weight  of 
the  finest  white  bronze-powder.  The  particles  of  this  pow- 
der, being  composed  almost  wholly  of  tin,  when  immersed 
in  a  solution  of  sulphate  of  copper,  dissolve,  and  coat  them- 
selves with  copper  by  the  simple  immersion  process,  and 
also  cause  those  of  black-lead  in  contact  with  them  to  be- 
come coated,  and  thus  a  thin  deposit  of  copper  is  very 


2 1 8  The  A  rt  of  Electro-Metallurgy. 

quickly  formed  all  over  the  bronzed  surface.  This  effect 
will  of  course  take  place  without  connecting  the  mould 
with  the '  battery,  but  they  may  be  immediately  connected 
together,  and  a  deposit  will  spread  over  the  whole  of  the 
bronzed  surface  by  the  ordinary  battery  process,  through 
the  medium  of  the  bronze  and  the  thin  deposit  already  men- 
tioned, and  it  may  be  continued  to  any  required  thickness  in 
the  usual  way.  By  this  plan,  gutta-percha  medallions  were 
repeatedly  covered  with  a  deposit  of  copper,  in  from  two  to 
five  minutes,  which  would  occupy  from  twenty  to  forty-five 
minutes  when  prepared  by  black-lead  in  the  usual  manner. 
The  addition  of  white  or  tin  bronze,  causes  the  deposit  to 
spread  as  rapidly  as  when  the  surface  is  prepared  by  the 
phosphorus  solution,  but  without  the  disadvantage  which 
occurs  in  using  the  latter,  of  making  the  deposited  metal 
brittle.  Silver  may  be  deposited  nearly  as  easily  as  copper 
upon  black-leaded  surfaces,  but  it  must  be  remembered  that 
wax  moulds  are  injured  in  a  cyanide  of  potassium  solution, 
and  should  be  protected  by  a  layer  of  copal  varnish  on  the 
parts  not  to  be  coated. 

For  moulds  of  elastic  composition,  the  depositor  may 
employ  the  following  liquids,  patented  by  Mr.  Alexander 
Parkes  :  A,  the  phosphorus  solution  :  to  make  nearly  three 
ounces  of  this,  melt  sixty-four  grains  of  beeswax  or  tallow ; 
then  dissolve  eight  grains  of  india-rubber  (cut  up  very  small), 
in  1 60  grains  of  bisulphide  of  carbon,  and  when  it  is  dissolved, 
add  to  it  very  carefully  (as  it  is  highly  inflammable)  the 
melted  wax,  and  stir  the  mixture  thoroughly  ;  then  dissolve 
sixty-four  grains  of  phosphorus,  in  960  grains  (about  two  and 
a  quarter  ounces)  of  bisulphide  of  carbon,  and  add  to  it 
eighty  grains  of  spirit  of  turpentine,  and  sixty-four  grains  of 
asphalte  in  fine  powder  ;  when  they  are  dissolved,  add  this 
solution  to  the  previous  one  of  india-rubber  and  wax,  and 
thoroughly  mix  them  by  shaking.  B,  the  silver  solution  : 
dissolve  thirty  grains  of  nitrate  of  silver  in  a  pint  (twenty 
ounces)  of  distilled  water.  And,  C,  the  gold  solution— to 


Preparing  Non-Metallic  Surf  aces  for  Deposits.   219 

make  twenty  ounces  of  which,  dissolve  five  or  six  grains  of 
pure  gold,  in  about  twenty  or  twenty-five  grains  of  a  hot 
mixture,  of  one  measure  of  nitric  acid,  and  two  or  three 
of  hydrochloric  acid,  and  when  dissolved,  dilute  the  solution 
with  twenty  ounces  of  distilled  water. 

In  making  surfaces  conductive  by  this  plan,  the  article, 
after  the  conducting  and  guiding  wires  are  attached  to  it,  is 
either  dipped  into  the  phosphorus  solution,  or  its  surface  is 
covered  with  that  liquid;  and  after  it  has  been  drained, 
it  is  allowed  to  remain  until  perfectly  dry ;  the  silver  solution 
is  next  applied  to  it,  and  is  drained  away  in  like  manner  for 
several  minutes,  until  the  surface  acquires  a  metallic  lustre  like 
black  china ;  it  is  then  gently  rinsed  with  distilled  water,  and 
the  gold  solution  applied  in  the  same  way,  which  gives  it  a 
yellowish  aspect:  after  an  other  rinsing  in  distilled  water,  it  is 
ready  for  receiving  a  deposit. 

The  same  patentee,  includes  in  his  patent  a  phosphorus 
moulding  composition,  by  the  use  of  which  the  immersion 
in  the  phosphorus  liquid,  is  dispensed  with,  the  moulds 
themselves  containing  the  required  amount  of  phosphorus. 
To  make  about  one  pound  of  this  composition,  melt  together 
half  a  pound  each  of  wax  and  deer's  fat,  then  dissolve  nine- 
teen or  twenty  grains  of  phosphorus  in  about  300  grains  of 
bisulphide  of  carbon ;  keep  the  wax  mixture  barely  melted, 
and  add  the  phosphorus  solution  slowly  to  it,  with  brisk 
stirring  of  the  fat,  pouring  it  in  at  the  bottom  of  the  melted 
mixture  by  means  of  a  vessel  with  a  long  spout,  to  prevent 
its  inflaming.  It  is  highly  dangerous  to  have  spilt  portions 
of  the  phosphorus  composition  or  solution  in  contact  with 
wood,  paper,  rags,  etc.,  or  other  fibrous  or  porous  substances, 
as  after  a  lapse  of  some  time  (even  hours),  they  will  often 
burst  into  flame. 

Another  method  of  rendering  the  surface  of  the  article 
conductive,  is  to  wet  it  with  a  solution  of  nitrate  of  silver, 
and  then  expose  it  to  sulphuretted  hydrogen  gas ;  this  con- 
verts the  film  of  silver  salt  into  a  conducting  substance,  viz., 


220  The  A  rt  of  Electro-Metallurgy. 

sulphide  of  silver  ;  the  liberated  nitric  acid  should  then  be 
removed,  by  dipping  the  article  in  distilled  water.  Or,  wet  it 
either  with  nitrate  of  silver  or  chloride  of  gold  solution,  and 
then  expose  it  to  hydrogen  gas;  this  reduces  the  salts  to 
metals.  The  article  must  then  be  rinsed.  The  film  of  silver 
salt  may  also  be  reduced  to  metal,  by  placing  the  object  in  a 
well  closed  box.  containing  at  its  lower  part  a  porcelain  dish 
containing  a  small  quantity  of  a  strong  solution  of  phosphorus 
in  bisulphide  of  carbon.  In  a  few  hours  the  vapour  will  re- 
duce the  salt  to  a  film  of  black  silver. 

Non-conducting  surfaces  may  also  be  rendered  conduct- 
ive by  washing  them,  first,  with  a  mixture  composed  of  equal 
parts  of  white  of  egg,  and  a  saturated  solution  of  common 
salt ;  second,  with  a  strong  solution  of  argentic  nitrate,  and 
exposing  them  to  sunlight  until  they  are  quite  black ;  and, 
third,  with  a  saturated  solution  of  green  vitriol.  (R.  Piffard, 
'  Chem.  News/  vol.  ii.  p.  323.)  Or  by  coating  the  surface 
with  a  film  of  gum -water,  and  drying ;  then  with  a  solution  of 
the  nitrate,  and  drying ;  and  then  exposing  it  to  sulphuretted 
hydrogen  gas.  (R.  Piffard,  *  Chem.  News,'  vol.  iii.  p.  no.) 

Hockin  recommended,  for  metallising  the  surfaces  of 
non-metallic  bodies,  to  plunge  them  into  iodised  collodion, 
then  immerse  them  in  a  nitrate  of  silver  solution,  expose 
them  to  the  light  for  a  few  seconds,  and  then  precipitate  the 
silver  in  a  metallic  state  by  means  of  a  bath  of  protosulphate 
of  iron  acidulated  with  nitric  acid,  and  finally  deposit  copper 
upon  them  in  a  nearly  neutral  solution  of  cupric  sulphate. 
('The  Chemist,'  New  Series,  vol.  i.  part  4,  January  1854, 
p.  196.)  Liquids  used  for  dyeing  hair  black,  composed  of 
a  solution  of  ammonio-nitrate  of  silver,  followed  by  one  of 
pyrogallic  acid,  might  be  similarly  employed. 

In  preparing  a  gypsum  mould,  Professor  Heeren  soaks  it 
in  wax,  then  covers  it  thickly  with  a  mixture  of  a  solution  of 
one  gramme  of  argentine  nitrate,  dissolved  in  two  grammes 
of  water,  to  which  two  and  a  half  grammes  of  aqueous 
ammonia  is  next  added;  and  then  also  three  grammes  of 


Preparing  Non-Metallic  Surfaces.  221 

absolute  alcohol.  The  mould  is  then  exposed  to  sulphuretted 
hydrogen  gas.  By  employing  four  or  five  Daniell's  cells,  the 
copper  spreads  quickly.  ('Journal  of  Chemical  Society/ 
vol.  x.  p.  1133.) 

Berland  prepares  non-conducting  surfaces  for  receiving  a 
deposit  thus  : — Wet  the  article  with  spirit  of  wine,  wash  it 
with  distilled  water,  and  whilst  wet,  pour  over  it  a  solution 
of  one  part  of  nitrate  of  silver  in  four  parts  of  distilled  water. 
After  draining  it  a  few  minutes,  a  solution  of  one  part  of  pure 
green  vitriol  in  three  parts  of  distilled  water  is  poured  upon 
it.  After  five  minutes,  repeat  with  the  silver  solution,  and 
then  with  the  green  vitriol,  three  or  four  times,  till  the  surface 
of  reduced  silver  has  a  whitish-grey  colour.  Then  wash  it 
with  pure  water,  and  it  is  ready  to  receive  the  deposit.  At  the 
first  moment  of  immersion,  the  entire  surface  is  covered  with 
a  thin  layer  of  copper  ('  Philosophical  Magazine,'  fourth  series, 
vol.  xxx.  p.  451.  See  also  Alexander  Jones's  patent,  1841). 

Coppering  lamp-posts,  &><;. — M.  Oudry  electro-deposits 
copper  upon  gas-lamps,  pillars,  candelabras,  fountains,  and 
ornamental  ironwork  generally.  He  first  coats  the  articles  with 
a  kind  of  red  paint  containing  benzine,  then  black-leads  the 
dried  paint,  and  deposits  copper  upon  it  to  the  thickness  of  one 
millimetre,  during  four  and  a  half  days,  by  the  battery  process. 
The  copper  is  afterwards  bronzed  by  applying  a  solution  of 
ammonio-acetate  of  copper. 

Coppering  fruit,  flou'ers,  insects,  reptiles,  &*c. — Objects  of 
this  kind,  some  of  which  will  scarcely  bear  handling,  are 
first  coated  with  silver  by  means  of  a  saturated  solution  of 
argentic  nitrate  in  hot  alcohol.  The  nitrate  is  reduced  to  fine 
powder  in  a  mortar,  and  an  excess  of  it  digested  with  alcohol 
in  a  flask  placed  in  warm  water,  with  occasional  shaking, 
until  the  liquid  is  saturated.  One  hundred  parts  of  alcohol, 
dissolve  about  two  and  a  quarter  parts  of  the  salt.  The  articles 
are  then  dipped  for  a  moment  in  the  warm  solution,  and  the 
liquid,  being  volatile,  soon  evaporates.  The  film  of  salt  left 
upon  the  objects,  is  reduced  to  metal  by  either  of  the  means 


222  The  A  rt  of  Electro-Metallurgy. 

already  described ;  the  articles  then  coated  in  the  solution  of 
cupric  sulphate,  and  either  silvered  or  gilded  as  may  be  desired. 

E.  T.  Noualhier  and  J.  B.  Prevost,  in  their  patent  of 
January  i,  1857,  propose  to  '  metallise  soft  surfaces — a  human 
corpse,  for  instance — by  the  following  process  : — All  the 
apertures  are  stopped  with  modeller's  wax,  the  body  is  placed 
in  a  suitable  attitude,  and  pulverised  nitrate  of  silver  spread 
over  it  by  means  of  a  brush  or  otherwise  ;  it  is  then  electro- 
coppered  in  a  bath  of  sulphate  of  copper  ; '  the  '  result  being 
a  metallic  mummy/ 

Coating  plaster  models  and  day  figures  with  copper. — Busts, 
and  other  similar  objects,  may  be  coated  by  saturating  them 
with  linseed-oil  (or  better,  with  beeswax),  then  well  black- 
leading,  or  treating  them  with  the  phosphorus,  silver,  and  gold 
solutions,  attaching  a  number  of  '  guiding  wires,'  connected 
with  all  the  most  hollow  and  distant  parts,  and  then  immersing 
them  in  the  sulphate  of  copper  solution,  and  causing  just  suffi- 
cient copper  to  be  deposited  upon  them  by  the  battery  process 
to  protect  them,  but  not  to  obliterate  the  fine  lines  or  features. 

Copying  wood  engravings  in  copper. — This  process  is  largely 
used.  In  cases  where  a  great  number  of  impressions  of  a 
particular  woodcut  is  required,  the  plan  of  taking  copies  of 
the  engraved  wooden  block  in  copper  by  the  electro  process, 
and  using  those  copies  instead  of  the  original  block  to  print 
from,  has  attained  a  considerable  degree  of  importance  ;  the 
vignette  at  the  head  of  the  title-page  of  the  '  Illustrated 
News,'  the  title-page  of  '  Punch,'  many  of  the  large  engrav- 
ings in  the  '  Illustrated  News,'  and  even  the  illustrations  of 
some  of  the  penny  periodicals,  are  regularly  produced  in  this 
way.  To  copy  an  engraved  wooden  block,  the  surface  is  first 
either  black-leaded,  or  moistened  with  water,  and  firmly  sur- 
rounded by  a  shallow  frame  of  metal ;  a  thick  piece  of  gutta- 
percha,  more  than  sufficient  to  fill  the  enclosed  space,  and 
made  quite  soft  by  heat,  is  then  laid  upon  it,  commencing  its 
contact  at  the  centre  of  the  engraving,  and  proceeding  out- 
wards, so  as  to  exclude  all  air-bubbles ;  a  plate  of  cold  iron  is 


Copying  Wood  Engravings.  223 

then  laid  upon  the  gutta-percha,  and  the  whole  subjected  to 
gradually  increasing  pressure  as  the  substance  cools.  The 
block  and  its  copy  are  then  separated,  and  the  figured  surface 
of  thecopy  (with  the  main  connecting  wire  previously  attached) 
is  treated  in  the  usual  manner,  with  black-lead  (or  with  the 
phosphorus,  silver,  and  gold  solutions) ;  '  guiding-wires '  are 
then  affixed,  and  copper  deposited  upon  the  mould  in  a 
solution  of  sulphate  of  copper,  until  a  moderate  thickness 
of  deposit  is  obtained,  which  will  occupy  at  least  twelve  or 
eighteen  hours  ;  when  sufficiently  thick,  the  deposit  is  re- 
moved, its  back  made  rigid  by  a  layer  of  solder  or  type 
metal  (the  surface  being  previously  moistened  with  a  solu- 
tion of  chloride  of  zinc,  to  make  the  solder  adhere),  the  back 
is  planed  flat,  and  mounted  upon  a  block  of  wood  to  the 
height  of  the  type.  In  London  this  process  is  employed 
upon  a  large  scale,  some  of  the  copies  being  upwards  of  two 
feet  square.  Engravings  upon  steel  are  copied  in  an  exactly 
similar  manner.  In  some  instances,  successful  deposits  of 
large  '  Illustrated  News  '  engravings,  have  been  formed  and 
taken  off  in  eight  hours ;  but  this  can  only  have  been  effected 
by  the  most  perfect  black-leading,  keeping  the  solution  in 
excellent  condition,  and  working  it  with  the  maximum  of 
battery  power.  A  mould  of  electrotype  copper  of  the  *  Times ' 
newspaper  is  said  to  have  furnished  as  many  as  twenty 
millions  of  impressions  before  it  was  quite  worn  out. 

Copying  set-up  type  in  copper. — The  process  of  electrotyp- 
ing  has  been  gradually  encroaching  upon  that  of  stereotyping, 
and  has,  we  are  informed,  almost  superseded  that  process  in 
America.  The  plan  adopted,  is  similar  to  that  of  copying 
woodcuts,  viz.,  to  lay  a  sheet  of  softened  gutta-percha  upon 
the  surface  of  the  page  of  type  (which  is  previously  black- 
leaded),  and  subjecting  it  to  increasing  pressure  until  it  is 
cold ;  the  gutta-percha  copy  is  then  removed,  and  treated  as  in 
copying  wood  engravings.  The  advantages  of  electrotyping 
over  stereotyping  are  numerous :  the  metal  is  harder,  takes  a 
sharper  impression  of  the  mould,  and  delivers  the  ink  much 


224  The  Art  of  Electro-Metallurgy.  , 

more  rapidly  than  type  metal,  besides  being  a  cleaner 
process  ;  it  also  takes  up  less  ink,  and  consequently  the 
printed  pages  dry  more  quickly.  Both  woodcuts  and  letter- 
press, have  also  been  copied  in  plaster  of  Paris,  and  the 
deposit  of  copper  formed  upon  that ;  but  this  material  is 
much  inferior  to  gutta-percha  for  the  purpose.  In  deposit- 
ing copper  upon  moulded  surfaces  of  set-up  type,  the  deposit 
is  thin,  and  easily  broken,  where  there  are  lines  ;  to  prevent 
this,  the  lines  are  wetted  with  a  solution  of  nitrate  of  mercury, 
or  other  '  quicking'  liquid  (see  pp.  195,  323),  at  those  parts, 
and  then  deposited  upon  again. 

Moulding,  and  copying  coins,  &c.  —  Some  electro-de- 
positors confine  themselves  to  multiplying  printing  surfaces, 
some  to  plating  with  nickel,  others  to  plating  with  silver  and 
gilding,  to  which  latter  process  in  other  establishments,  is 
added  the  multiplication  of  works  of  art,  the  production  of 
busts,  statues,  &c.  The  electro-depositor,  therefore,  who 
includes  in  his  business  the  multiplication  of  works  of  art, 
as  well  as  the  simple  plating  of  metal  articles,  will  require  a 
knowledge  of  the  art  of  moulding. 

Ability  to  reproduce  works  of  art  on  a  large  scale, 
requires  very  considerable  experience,  and  amateurs  should 
first  acquire  ability  to  copy  smaller  ones,  such  as  medals, 
coins,  etc.  The  moulding  materials  commonly  used  for 
small  objects,  are  fusible  alloy,  wax,  stearine,  gutta-percha, 
plaster  of  Paris  ;  a  mixture  of  gutta-percha  and  marine  glue, 
a  composition  of  spermaceti,  etc.,  etc. 

Fusible  alloy,  consists  of  a  melted  mixture  of  eight  parts 
bismuth,  five  of  lead,  and  three  of  tin,  and  fuses  at 
about  the  temperature  of  boiling  water.  A  much  more 
fusible  mixture,  which  melts  at  151°  Fahr.,  consists  of  seven 
and  a  half  parts  of  bismuth,  four  of  lead,  two  of  tin, 
and  one  and  a  half  of  cadmium.  The  ingredients  should 
be  thoroughly  mixed  in  each  case.  The  melted  alloy  should 
be  poured  upon  a  slab  of  stone,  its  surface  skimmed  by 
means  of  a  card  ;  and  the  medal  or  coin  to  be  copied 


Moulding  Objects.  225 

dropped  upon  it.  As  soon  as  the  alloy  has  solidified,  the 
coin  may  be  removed  ;  the  end  of  a  clean  copper  wire  at- 
tached to  the  mould  by  means  of  heat,  the  back  of  the  alloy 
varnished,  and  the  copy  hung  in  the  solution  of  sulphate  of 
copper  to  receive  the  deposit- 

To  copy  a  medal  in  wax,  the  medal  (slightly  oiled) 
should  be  surrounded  by  a  rim  of  stiff  paper  about  one 
inch  deep,  fastened  by  means  of  sealing-wax;  then  made 
quite  warm,  and  the  white  wax  in  a  melted  state  (but  not 
too  hot),  poured  upon  it.  When  the  wax  has  become  solid, 
put  it  in  a  cold  place  for  several  hours,  and  then  separate 
the  coin  and  its  copy ;  but  if  the  medal  be  a  large  one,  the 
cooling  process  must  be  gradual,  otherwise  the  wax  may  split. 

A  good  composition  for  copying  coins,  consists  of 
two  parts  of  gutta-percha,  and  one  of  Jeffery's  marine 
glue.  The  two  substances  are  cut  up  very  small,  heated 
very  gradually,  with  constant  stirring,  until  most  tho- 
roughly mixed.  To  copy  both  sides  of  a  medal  in  this 
mixture,  take  a  strip  of  thin  sheet  copper,  brass,,  or  tinned 
iron,  about  an  inch  wide,  wind  it  closely  round  the  edge  of 
the  medal,  and  solder  its  ends  together  ;  wipe  the  medal, 
and  take  two  balls  of  the  composition,  quite  hot  and  soft, 
and  press  them  simultaneously  against  the  two  faces  of  the 
medal,  working  the  material  from  the  centre  towards  the 
circumference,  to  exclude  bubbles  of  air ;  place  two  thick 
plates  of  cold  metal,  one  on  each  side,  and  gradually  screw 
up  the  whole  in  a  vice  or  press,  gently  at  first,  but  in- 
creasing the  pressure  to  a  high  degree  as  the  materials  be- 
come hard.  When  it  is  quite  cold,  which  will  be  in  about 
two  hours,  the  two  copies  may  be  easily  removed  from  the 
original,  by  inserting  the  ends  of  gimlets  in  their  backs  and 
drawing  them  out  ;  they  are  easily  removed,  because  the 
composition  slightly  contracts  in  cooling.  They  will  present 
fine  impressions  of  the  original,  and  be  perfectly  free  from 
air-bubbles,  if  the  operation  has  been  carefully  performed. 
A  slight  disadvantage  attending  the  use  of  gutta-percha 

Q 


226  The  A  rt  of  Electro-Metallurgy. 

(and  mixtures  containing  it)  is,  that  it  shrinks  a  little,  in 
course  of  a  long  period,  but  unless  the  surface  is  a  large  one, 
this  defect  is  too  small  to  be  perceived 

All  these  mixtures  require,  of  course,  to  have  suitable 
conducting  wires  attached  to  them,  and  their  surfaces  black- 
leaded,  or  otherwise  prepared,  to  render  them  conductive ; 
and  those  parts  to  which  the  conducting  material  has  acci- 
dentally adhered,  and  which  are  not  to  be  coated,  must  be 
'  stopped  off'  by  means  of  a  suitable  varnish.  Quick-drying 
spirit  varnish  is  very  suitable  for  the  purpose,  especially  if 
some  superfine  red  sealing-wax  is  dissolved  in  it,  to  render  the 
coating  more  visible.  It  must  also  not  be  forgotten,  that  in 
all  cases,  the  copy  taken  of  an  original  object  is  not  a  fac- 
simile of  the  object,  but  its  reverse,  and  that  to  obtain  a 
fac-simile  we  must  take  a  copy  of  the  copy.  For  instance,  if 
we  take  a  mould  of  a  coin  in  copper,  either  by  means  of  elec- 
trolysis or  in  any  other  way,  we  must  take  a  copy  from  this 
mould  in  order  to  obtain  a  real  fac-simile. 

Copies  of  coins  may  also  be  taken  in  plaster  of  Paris. 
To  copy  a  coin  or  medal  in  plaster  it  should  be  slightly 
oiled,  and  surrounded  by  a  paper  rim  one  inch  in  depth. 
Take  the  finest  and  freshest  plaster  (which  has  been  kept  in 
a  well-closed  bottle),  mix  it  with  water  in  a  lipped  vessel,  to 
the  consistency  of  treacle,  then  without  delay  brush  a  little 
of  it  over  the  surface  of  the  coin  with  a  camel-hair  brush, 
and  at  once  pour  on  the  remainder.  The  plaster  quickly 
sets  to  a  solid  state,  and  soon  afterwards  may  be  removed 
from  the  medal.  The  mould  may  be  either  itself  copied 
in  wax,  etc.,  or  be  thoroughly  dried,  and  then  saturated  with 
wax  or  tallow,  by  standing  whilst  still  hot  in  a  shallow  layer 
of  the  melted  substance,  until  the  latter  has  spread  through- 
out its  mass,  and  then  at  once  remove  it,  and  prepare  its  sur- 
face for  receiving  a  deposit.  Or  it  may  be  prepared  for  black- 
leading  by  saturating  it  with  skimmed  milk,  and  then  drying  it. 

Copying  Busts,  Statuettes,  Statues,  &c. — There  are,  how- 
ever, many  objects  which  cannot  be  copied  by  any  fo  the 


Copying  Busts,  Statues,  &c.  227 

methods  above  described,  such  as  medals  which  are  'under- 
cut ' ;  busts,  statues,  and  figures  of  various  kinds,  because 
the  mould  formed  upon  the  object  cannot  be  removed  with- 
out breaking  either  the  original  or  its  copy.  In  such  cases 
either  the  mould  or  its  copy,  or  both,  are  formed  in  pieces, 
so  arranged  that  each  piece  may  be  removed  ;  or  the  copy 
of  the  object  is  taken  in  an  elastic  moulding  material,  which 
by  allowing  itself  to  be  stretched,  may  be  removed  from 
overhanging,  projecting,  and  undercut  parts  of  the  object, 
and  then  returns  to  its  original  form  and  dimensions.  The 
best  substance  of  this  kind,  and  almost  the  only  one  used,  is 
composed  of  four  parts  of  the  best  thin  glue  and  one  of 
treacle;  the  glue  is  broken  into  small  pieces,  and  soaked 
several  hours,  or  until  it  is  quite  soft,  in  sufficient  cold 
water  to  cover  it.  The  superfluous  water  is  then  thrown 
away,  and  the  gelatine  together  with  the  treacle,  is  heated  in 
a  glue-pot  (i.e.  by  immersing  the  vessel  in  boiling  water),  to 
nearly  100°  C,  and  stirred  until  the  two  substances  are 
thoroughly  mixed.  The  use  of  the  treacle  is  to  prevent  the 
mould  drying  and  shrinking.  Some  operators  add  half  an 
ounce  of  beeswax  for  each  pound  of  glue. 

The  great  disadvantage  of  such  moulds  is  their  ten- 
dency to  absorb  water,  to  swell,  and  to  be  partly  dissolved  in 
the  solution  of  sulphate  of  copper.  These  difficulties  are  over- 
come, by  using  a  depositing  liquid  containing  the  minimum 
proportion  of  water,  and  covering  the  mould  as  quickly  as 
possible  with  the  metallic  deposit,  any  portions  of  it  not 
requiring  a  deposit  being  previously  well  coated  with  a 
quickly- drying  varnish,  best,  a  solution  of  india-rubber  in 
bisulphide  of  carbon.  Various  attempts  have  been  made  to 
enable  the  gelatine  to  resist  more  perfectly  the  action  of  the 
water,  one  of  the  most  effectual  of  which  is  to  dissolve  in 
the  mixture,  two  parts  of  tannic  acid  for  each  100  parts  of 
the  dry  glue,  or  to  immerse  the  mould  a  few  seconds  in  a 
solution  of  ninety  parts  water  and  ten  of  bichromate  of 
potassium,  and  then  expose  it  to  the  sun. 

Q  2 


228  The  A  rt  of  Electro-Metallurgy. 

If  the  object  to  be  copied  is  a  medallion  with  undercut 
parts,  it  is  treated  thus  : — First  well  oil  the  medallion ;  then 
encircle  its  edge  by  a  strip  of  stout  paper,  and  pour  the 
mixture  (quite  hot,  and  of  the  consistency  of  treacle),  upon 
its  surface,  to  the  depth  of  half  an  inch  or  more,  according 
to  the  size  of  the  medal,  and  the  depth  of  its  hollow  parts, 
brushing  its  surface  beneath  the  liquid  with  a  brush  having 
fine  and  long  hairs,  to  remove  air-bubbles.  Allow  the  mix- 
ture to  remain  until  it  is  quite  firm,  which  will  be  from  two 
to  twenty-four  hours,  according  to  its  bulk  ;  take  off  the 
paper,  and  remove  the  mould  very  gently,  carefully  stretch- 
ing and  drawing  it  at  the  same  time  in  the  direction  of  the 
overhanging  parts,  to  prevent  injury. 

Should  the  object  to  be  copied  be  a  hollow  metallic  bust, 
proceed  as  follows  : — First  oil  it,  then  partly  fill  it  with  sand, 
to  make  it  heavy,  and  thus  prevent  its  rising  in  the  liquid, 
and  cover  its  opening  by  fixing  a  piece  of  millboard  strongly 
over  it ;  then  place  the  bust  in  the  centre  of  a  circular  and 
taper  vessel,  a  few  inches  deeper  and  wider  than  itself,  and 
pour  the  melted  composition  in  steadily,  until  it  is  a  few 
inches  above  the  top  of  the  head,  tapping  the  bust,  and  in- 
clining the  outer  vessel,  to  facilitate  the  escape  of  air-bubbles. 
The  composition  will  become  firm  in  about  twenty  hours, 
and  may  be  easily  removed  from  the  vessel  by  shaking, 
if  the  latter  has  been  previously  well  oiled ;  the  mould  may 
then  be  extracted  from  the  bust,  by  previously  marking  on  its 
lower  end  the  position  of  the  face,  passing  a  knife  carefully 
up  the  back  of  the  bust  nearly  to  the  crown  of  the  head, 
and  opening  the  elastic  mould  with  the  hands  whilst  a  second 
person  lifts  out  the  bust.  If  the  original  bust  is  composed 
of  plaster,  it  must  be  previously  saturated  with  oil,  to  prevent 
the  melted  composition  adhering  to  it.  In  all  cases,  after 
fixing  the  necessary  conducting  and  guiding  wires  to  an 
elastic  mould,  it  is  rendered  conducting  by  means  of  the 
silver  or  gold  solutions,  reduced  to  metal  by  means  of  phos- 
phorus or  hydrogen,  &c. 


Electro-Deposited  Statues.  229 

Notwithstanding  the  greatest  possible  care  naving  been 
taken  in  making  and  copying  an  elastic  mould,  failures  are 
not  infrequent ;  either  the  coating  of  deposited  metal  is 
imperfect  in  the  inmost  parts  of  the  mould,  or  the  latter 
swells  so  greatly  as  to  alter  the  figure  of  the  object  Some 
objects  are  first  copied  in  elastic  composition,  then  the  elastic 
mould  re- copied  in  the  phosphorus  and  wax  mixture  at  the 
lowest  possible  temperature,  so  as  not  to  melt  the  gelatine  ; 
the  mould  removed,  and  the  other  deposited  upon. 

Bubbles  of  air  often  adhere  to  moulds  immersed  in  de- 
positing solutions  ;  they  may  be  prevented  by  previously 
dipping  the  object  in  spirit  of  wine;  or  be  removed  by  the  aid 
of  a  soft  brush,  or  by  directing  a  powerful  upward  current  of 
the  liquid  against  them  by  means  of  a  vulcanized  india-rubber 
bladder,  with  a  long  and  curved  glass  tube  attached  to  it  ; 
but  the  liquid  should  be  free  from  sediment. 

With  large  objects,  such  as  statues,  a  different  plan  from 
any  of  those  already  described  is  resorted  to  ;  in  this  case, 
instead  of  employing  elastic  moulds,  the  copy  itself  is  sacri- 
ficed. The  original  figure,  formed  of  plaster  of  Paris,  and 
obtained  from  a  modeller  or  sculptor,  is  saturated  all  over 
its  surface  with  boiled  linseed  oil.  It  is  then  coated  with 
extreme  care  in  all  parts  with  a  shining  film  of  black-lead, 
by  prolonged  blushing,  or  with  a  film  of  silver  by  means  of 
the  phosphorus  and  silver  solutions;  but  the  presence  of 
phosphorus  is  apt  to  make  the  deposited  copper  brittle.  It 
is  then  immersed  in  a  large  cistern  of  the  sulphate  of  copper 
solution  (see  p.  206),  and  coated  entirely  with  copper  to  a 
thickness  of  about  yVtn  °f  an  mcn,  or  sufficiently  to  retain  its 
form  when  the  inner  figure  is  removed.  It  is  now  lifted 
out  of  the  vat,  washed,  the  copper  cut  through  at  suitable 
places,  the  plaster  figure  broken  away  with  great  care, 
and  the  whole  of  it  extracted.  The  outer  surfaces  of  the 
copper  forms,  (with  wires  attached)  are  now  thoroughly 
varnished  all  over,  to  prevent  any  deposit  being  formed 
thereon;  the  forms  exposed  to  sulphuretted  hydrogen,  or 


230  The  A  rt  of  Electro-Metallurgy. 

dipped  into  a  weak  solution  of  sulphide  of  potassium,  to 
prevent  adhesion  of  the  deposit ;  the  parts  immersed  in  the 
depositing  vat  again,  and  filled  with  copper  solution.  A  dis- 
solving plate  of  pure  electrotype  copper  is  suspended  within 
each  portion,  and  a  deposit  of  copper  thus  formed  all  over  its 
interior,  until  a  considerable  thickness,  varying  from  J  to  J-  of 
an  inch,  is  deposited,  which  requires  a  period  of  three  or  four 
wreeks.  Each  piece  is  now  removed  from  the  liquid,  washed, 
and  the  outer  shell  torn  off,  when  all  the  parts  of  the  figure 
remain  nearly  complete  and  ready  for  fixing  together.  Some 
of  the  objects  made  by  this  process  by  Messrs.  Elkington  are 
colossal ;  that  of  the  Earl  of  Eglinton  is  13 J  feet  high,  and 
weighs  two  tons  ;  and  the  vat  in  which  it  was  formed,  is 
15  feet  long,  9  feet  deep,  and  8  feet  wide,  and  is  capable  of 
containing  6,680  gallons  of  liquid.  Messrs  Christople  of  Paris, 
made  a  statue  of  9  metres  (=29  feet  6  in.)  high,  weighing 
3,500  kilogrammes  (=atout3  tons  9  cwt),  and  of  a  thick- 
ness of  4-|  millimetres.  It  occupied  about  ten  weeks  in 
depositing.  As  it  is  difficult  in  practice  to  deposit  the  figures 
of  a  man,  horse,  &c.  all  in  one  piece,  this  plan  of  dividing  the 
first  copper  figure  in  suitable  parts,  usually  at  the  lower  edge 
of  the  vest,  the  shoulders  and  wrists,  and  depositing  upon 
the  interiors  of  these,  and  fastening  the  separate  deposits  to- 
gether to  form  the  complete  figure,  is  nearly  always  adopted. 
Lenoir  employs  a  different  process,  which  may  be  briefly 
stated  as  follows  : — An  external  copy  of  the  figure  is  made 
of  gutta-percha  in  several  parts,  so  as  to  be  capable  of  being 
put  together  and  form  the  complete  figure ;  and  the  internal 
surfaces  of  these  pieces  are  black-leaded.  An  outline  figure 
of  the  object,  but  of  somewhat  smaller  dimensions,  is  formed 
of  platinum  wire,  to  act  as  an  anode,  and  the  pieces  of  gutta- 
percha  are  fixed  together  to  form  the  complete  figure  around 
it.  The  mould  is  placed  in  a  vertical  position,  the  platinum 
outline  figure  being  suspended  in  it  by  means  of  its  connecting 
wires,  and  prevented  from  touching  the  mould  by  partly 
covering  the  wire  with  a  spiral  of  india-rubber  thread.  The 


Etching  Copper  Plates.  231 

mould  and  its  anode  (previously  weighted)  are  now  immersed 
in  the  same  vertical  position  in  the  copper  solution,  the 
battery  connected,  and  a  current  of  the  liquid  caused  to  con- 
tinually enter  the  mould  by  a  hole  at  the  top  of  the  head 
and  escape  by  two  holes  at  the  feet.  After  a  sufficient 
deposit  is  formed,  the  flexible  anode  of  wire  is  drawn  out 
through  the  hole  in  the  head,  the  parts  of  the  gutta-percha 
mould  are  taken  asunder,  and  the  seams  in  the  copper  at 
the  junctions  of  the  model  are  then  removed  by  filing,  &C.1 

Glyptography. — The  process  of  glyphography  consists 
in  coating  a  plate  of  copper  with  two  thin  layers  of  en- 
graver's wax  composition,  the  first  one  white,  and  the  second 
black,  engraving  the  design  through  the  wax  to  the  copper 
beneath,  then  black-leading  the  entire  surface  of  the  wax, 
varnishing  the  back  of  the  copper  plate,  and  depositing  copper 
upon  the  entire  front  surface  until  a  stout  plate  of  metal  is 
formed.  The  plate  is  then  removed,  strengthened  with  solder, 
mounted  like  a  stereotype  plate,  and  employed  for  printing 
in  the  usual  manner.  Before  black-leading,  it  is  sometimes 
necessary  to  thicken  the  wax  coating  over  large  white  spaces, 
the  middle  portions  of  which  might  otherwise  print  black. 

Etching  copper  plates. — In  etching  a  copper  plate  by 
galvanism,  we  first  solder  a  wire  to  it,  then  varnish  the 
back,  and  cover  the  front  with  a  thin  layer  of  engraver's 
etching-ground  ;  draw  the  design  upon  the  front  surface 
with  an  etching  needle,  cutting  through  this  material  to  the 
clean  surface  of  the  copper.  Having  completed  the  etching, 
hang  the  plate  as  an  anode  in  the  ordinary  sulphate  of 
copper  solution,  opposite  a  suitable  cathode  of  copper. 
The  current  of  electricity  in  passing  out  of  the  engraved 
lines  into  the  liquid,  causes  the  copper  in  them  to  dissolve, 
and  thus  etches  the  design  on  the  plate.  The  various 
gradations  of  light  and  shade  are  produced  by  suspending 
cathodes  of  different  forms  and  sizes  opposite  the  plate  to 

1  M.  Plante  employs,  insten^  of  the  platinum  wire  outline,  a  thin 
.hollow  anode  of  lead  pierced  with  holes. 


232  The  A  rt  of  Electro- Metallurgy. 

be  etched,  in  varied  positions,  and  at  different  distances  from 
it,  thus  causing  the  plate  to  be  corroded  to  unequal  depths 
in  different  parts,  the  deepest  action  being  always  at  those 
portions  of  the  electrodes  which  are  nearest  together. 

Depositing  copper  upon  glass,  &c. — The  only  effectual 
way  of  obtaining  an  adhesive  deposit  upon  glass  or  por- 
celain, is  to  send  the  article  to  a  glass  and  porcelain  gilder, 
and  have  gold  burnt  into  its  surface,  and  then  depositing 
upon  the  gold  coating  in  the  usual  manner. 

1 6.  Nickel.— Elec.  chem.  eqt.=  ^  =  29-5.  The  com- 
monest salts  of  nickel,  are  the  oxide,  nitrate,  chloride,  car- 
bonate, and  sulphate.  The  oxide  is  a  black  powder, 
soluble  in  nitric,  hydrochloric,  and  sulphuric  acids  j  the 
nitrate  and  chloride  are  green  salts  freely  soluble  in  water  ; 
the  carbonate  is  a  pale  green  powder  readily  soluble  in  most 
acids  ;  the  sulphate  is  a  freely  soluble  salt.  The  oxide  may 
be  made  by  heating  the  carbonate  or  nitrate  to  redness,  or 
by  precipitating  a  solution  of  a  salt  of  nickel  with  caustic 
potash  or  soda.  The  nitrate  may  be  made  by  digesting 
the  metal,  its  oxide  or  carbonate,  in  dilute  nitric  acid,  and 
evaporating  the  solution ;  the  chloride  may  be  formed  with 
hydrochloric  acid  in  a  similar  manner,  or  by  adding  an 
excess  of  that  acid  to  a  solution  of  the  nitrate,  and  evaporat- 
ing the  mixture  to  dryness.  The  carbonate  may  be  formed 
by  adding  a  solution  of  carbonate  of  sodium  to  one  of  any 
salt  of  nickel,  and  washing  and  drying  the  precipitate.  The 
sulphate  may  be  made  by  digesting  either  the  oxide,  nitrate, 
chloride,  or  carbonate  in  an  excess  of  dilute  sulphuric  acid, 
and  evaporating  the  solution  nearly  to  dryness.  A  solution 
of  the  nitrate,  chloride,  or  sulphate,  may  also  be  obtained  by 
making  a  bar  of  nickel  (or  fragments  of  nickel,  suspended 
on  platinum  wire  gauze)  the  anode  in  dilute  nitric,  hydro- 
chloric, or  sulphuric  acid,  and  passing  the  current  until  the 
acid  is  sufficiently  saturated  with  metal. 

Electrolysis  of  salts  of  nickel. — I  have  electrolysed  dilute 


Electrolysis  of  Salts  of  Nickel.  233 

hydrochloric  acid  by  means  of  one  Smee's  element,  an  anode 
of  nickel  and  a  cathode  of  copper.  The  conduction  was  very 
feeble,  and  a  film  of  iron  grey  metal  was  deposited  upon  the 
cathode  in  twelve  hours.  A  dilute  solution  of  nitrate  of 
nickel  did  not  yield  its  metal  freely.  By  making  a  strong 
solution  of  salammoniac,  or  of  sulphate  of  ammonium,  and 
passing  a  strong  current  through  it,  by  means  of  an  anode  of 
nickel  during  several  hours,  until  the  liquid  acquired  a  pale 
greenish  blue  colour,  I  obtained  a  deposit  of  coherent  white 
metal.  A  good  solution  for  depositing  nickel,  is  the  double 
cyanide  of  nickel  and  potassium,  to  which  some  common 
salt  has  been  added. 

Nickel  has  also  been  deposited  from  a  liquid  formed  by 
precipitating  a  solution  of  nitrate  of  nickel  with  carbonate 
or  cyanide  of  potassium,  washing  the  precipitate  and  dis- 
solving it  nearly  to  saturation  in  a  solution  of  potassic 
cyanide,  and  operating  upon  the  liquid  by  the  battery 
process  with  an  anode  of  nickel.  The  metal  deposited  from 
this  solution  is  said  to  be  nearly  equal  in  whiteness  to  silver. 
According  to  Smee,  a  solution  of  chloride  of  nickel  is  an 
excellent  one  for  deposition,  because  of  its  small  tendency 
to  evolve  hydrogen  at  the  cathode.  The  nickel  deposited 
from  it  '  has  a  peculiar  white  brilliant  lustre,  looking  almost 
like  glass ;  this  deposit  is  so  very  beautiful,  though  brittle 
when  removed  from  the  negative  pole,  that  its  examination 
would  amply  repay  any  person  taking  the  trouble  to  precipi- 
tate it.'  He  also  states  that  a  solution  of  the  acetate  yields 
a  black  powder  deposit,  and  is  a  bad  one  for  obtaining 
reguline  metal. 

Merrick  has  electrolysed  a  number  of  solutions  of  salts 
of  nickel  by  means  of  a  current  from  two  Grove's  cells,  an 
anode  of  nickel  and  a  cathode  of  platinum,  placing  a  volta- 
meter for  mixed  gases  in  the  circuit  to  measure  the  strength 
of  the  current,  and  a  rheostat  to  keep  the  current  uniform. 
He  weighed  the  metallic  deposits.  The  nitrate  yielded  a 
thick  greenish  non-metallic  deposit  (probably  a  basic 


234  The  A  rt  of  Electro-Metallurgy. 

nitrate),  with  a  metallic  layer  beneath.  A  solution  of  sp.  gr. 
1-0503  of  the  pure  chloride,  yielded  an  adherent  deposit  of 
metal  with  a  non-adherent  layer  of  black  powder  upon  it. 
The  quantity  of  metal  obtained  equalled  83-6  per  cent  of 
the  theoretical  amount.  With  a  solution  of  commercial  sul- 
phate of  nickel,  there  was  a  great  evolution  of  gas  from  the 
cathode,  and  much  from  the  anode;  and  two  layers  of 
deposit,  the  outer  one  greenish  and  non-adherent,  the  lower 
one  speckled  and  blotched  metal.  A  solution  of  sp.  gr. 
1-0223  of  the  pure  sulphate,  gave  a  blackish  deposit  of 
metal,  equalling  52  per  cent  of  the  theoretical  amount, 
streaked  with  a  non-adherent  greenish  deposit  of  subsul- 
phate  above  it.  With  a  solution  of  sp.  gr.  1-0232  of  the 
acetate,  much  of  the  deposit  was  black  oxide  in  powder. 
The  coherent  metallic  layer  beneath,  equalled  10  per  cent 
of  the  theoretical  amount.  A  solution  of  the  cyanide  of 
nickel  and  potassium,  evolved  much  gas  at  the  cathode, 
and  gave  a  dull  blackish-grey  metallic  deposit  equal  to  14 
per  cent  of  the  theoretical  quantity.  One  of  the  ammonio- 
nitrate,  of  sp.  gr.  roi6,  yielded  a  variously  coloured 
metallic  deposit  amounting  to  97-4  per  cent  of  the  theore- 
tical amount,  beneath  a  layer  of  greenish  subsalt.  The 
double  chloride  of  nickel  and  ammonium,  gave  a  pulverulent 
deposit,  with  a  metallic  one  beneath,  equal  to  47  per  cent 
of  the  theoretical  quantity.  The  ammonio-chloride  yielded 
96  per  cent  of  the  required  quantity  of  metal,  partly  bright, 
and  partly  dull.  The  double  sulphate  of  nickel  and 
ammonium,  gave  a  good  metallic  deposit,  equalling  93 -5  per 
cent  of  the  theoretical  amount.  The  ammonio-sulphate 
gave  96  per  cent  in  the  form  of  greyish-brown  metal;  the 
solution  was  formed  by  adding  an  excess  of  ammonia,  and 
then  alcohol,  to  a  strong  solution  of  nickel  sulphate,  and 
dissolving  the  precipitated  salt  in  water.  A  solution  of  the 
pure  sulphate  of  nickel  and  potassium,  evolved  much  gas 
from  the  cathode,  and  gave  a  blackish-green  deposit,  with  a 
dull  metallic  layer  beneath.  The  layer  of  metal  contained 


Nickel- Plating  by  Simple  Immersion  Process.    235 

3  7  per  cent  of  the  theoretical  amount  of  nickel.  (£  Chem. 
News,'  vol.  xxvi.  p.  209;  also  'Journal  of  the  Chemical 
Society,'  vol.  xi.  p.  204.)  A  solution  of  hydrated  oxide  of 
nickel,  in  a  mixture  of  cream  of  tartar,  and  a  little  soda  and 
water,  electrolysed  by  means  of  a  current  from  two  Daniell's 
cells  and  platinum  electrodes,  yields  a  layer  of  solid  hydrated 
peroxide  of  nickel  upon  the  anode  (W.  Wernicke,  '  Journal 
of  the  Chemical  Society/  vol.  ix.  p.  307). 

Deposition  of  nickel  by  simple  immersion. — Nickel  is  not 
usually  deposited  by  simple  immersion  process  in  aqueous 
solutions ;  it  is  too  electro-positive.  Crystalline  silicon 
separates  nickel  from  its  anhydrous  fluoride  by  the  assist- 
ance of  heat.  I  mixed  1*5  grain  of  crystals  of  silicon 
with  ten  of  dry  fluoride  of  nickel,  and  heated  the  mixture. 
At  a  gentle  red  heat  in  a  porcelain  crucible,  vivid  incan- 
descence occurred,  and  metallic  nickel  was  deposited  and 
melted  by  the  evolved  heat.  The  globules  were  grey, 
looked  like  nickel,  and  were  feebly  attracted  by  a  magnet, 
I  also  immersed  crystals  of  silicon  in  an  aqueous  solution 
of  fluoride  of  nickel  containing  free  hydrofluoric  acid  ;  the 
crystals  did  not  coat  themselves  with  metal.  According  to 
I.  C.  Davies,  nickel  is  scarcely  precipitated  at  all  from  acid 
solutions  by  means  of  zinc;  but  if  ammonia  be  added  to  the 
liquids,  precipitation  occurs.  Zinc  throws  down  the  metal 
perfectly  from  a  solution  of  nickel  chloride  rendered  ammo- 
niacal.  A.  Merry  obtained  similar  results  with  sulphate 
solutions  ('  Journal  of  the  Chemical  Society/  vol.  xiii.  p.  31 1). 
According  to  M.  Becquerel,  the  simple  immersion  of  copper 
in  a  solution  of  the  double  chloride  of  nickel  and  sodium, 
is  sufficient  to  deposit  the  metal  ('  The  Chemist/  vol.  v.  p. 
408).  Magnesium  deposits  hydrated  protoxide  of  nickel 
from  a  solution  of  nickel  sulphate  (Commaille,  '  Chemical 
News/  vol.  xiv.  p.  1 88).  But  from  slightly  acid  solutions  of 
salts  of  protoxide  of  nickel,  magnesium  deposits  hydrogen 
and  metallic  nickel  (Roussin,  '  Chemical  News/  vol.  xiv. 
p.  27). 


236  The  A  rt  of  Electro-Metallurgy. 

Depositing  nickel  by  contact  with  another  metal  (see  also 
p.  82). — C.  Mene  coats  articles  of  iron,  steel,  copper,  brass, 
zinc,  and  lead,  by  immersing  them  in  contact  with  zinc,  in 
a  boiling  neutral  solution  of  chloride  of  zinc,  containing 
metallic  nickel  in  fragments  or  plate.  If  the  solution  is  acid, 
the  coating  will  be  dull  ('  Chemical  News,'  vol.  xxv.  p.  214). 
Stolba  adds  two  measures  of  water  to  one  of  concentrated 
solution  of  chloride  of  zinc  in  a  copper  vessel,  boils  the 
mixture,  and  re-  dissolves  any  precipitate  by  the  least  possible 
quantity  (a  few  drops)  of  hydrochloric  acid.  A  few  particles 
of  powdered  zinc  are  thrown  into  the  liquid ;  and  this  causes 
a  deposit  of  zinc  upon  the  vessel.  Sufficient  chloride  or  sul- 
phate of  nickel  is  then  added  until  the  liquid  is  distinctly 
green;  and  the  previously  cleaned  articles  are  at  once 
immersed  in  contact  with  zinc  in  the  boiling  liquid  during 
fifteen  minutes.  For  thick  coatings  the  operation  is  repeated. 
Articles  of  zinc,  cast  iron,  wrought  iron,  steel,  brass,  and 
copper,  are  coated  by  this  process.  According  to  Raoult, 
gold  in  contact  with  nickel,  either  in  a  cold  or  boiling,  acid 
or  neutral,  solution  of  salts  of  nickel,  receives  no  metallic 
deposit  ('Journal  of  the  Chemical  Society,'  vol.  xi.  p.  465). 

Depositing  nickel  by  separate  current  process  (see  also 
p.  89). — Nickel  is  not  usually  deposited  by  the  single  cell 
method,  because  that  process  robs  the  liquid  of  metal, 
and  sets  free  its  acid,  and  an  acid  solution  of  nickel  is 
difficult  to  manage.  Various  solutions  have  been  tried  for 
practical  use  by  the  separate  current  method,  but  the  most 
successful  ones  have  been  those  composed  of  the  double 
salts  of  nickel  and  ammonium.  In  the  year  1 855  I  employed 
the  double  salts  of  nickel  and  ammonium  for  depositing  the 
metal,  and  published  the  results  of  the  use  of  them.  In 
August  1869  Dr.  Isaac  Adams  patented  those  salts  for  nickel 
plating  purposes,  and  nearly  all  the  deposition  of  nickel  has 
been  done  by  their  aid.  The  liquids  contain  various  pro- 
portions of  the  salts  to  the  water,  but  are  usually  strong. 

The  credit  of  depositing  nickel  upon  a  large  scale,  and 


Nickel- Plating  Solutions.  237 

coating  other  metals  extensively  with  it,  has  been  given  to 
Dr.  Adams  (see  'Chemical  News/  vol.  xxi.  p.  69).  According 
to  the  terms  of  his  patent  he  claims  that  the  solution  must 
be  free  from  potash,  soda,  lime,  alumina,  and  nitric  acid ; 
according  also  to  M.  Gaiffe  it  should  not  contain  a  trace  of 
salt  of  potash  or  soda ;  but  Becquerel  disproves  this,  and 
shows  that  the  double  sulphates  of  potassium  and  nickel, 
may  be  used  with  equal  success  to  those  of  ammonium  and 
nickel  ;  and  that  the  bath  must  not  be  allowed  to  become 
acid  (' Chemical  News/  vol.  xxi.  p.  57).  H.  Bouillet  also 
denies  the  necessity  of  absence  of  the  fixed  alkalies  in 
depositing  nickel,  and  says  :  '  I  have  deposited  good  nickel 
from  the  double  sulphate  of  nickel  and  magnesium' 
('Chemical  News/  vol.  xxii.  p.  22). 

Becquerel  employed  a  solution  of  sulphate  of  nickel,  with 
its  free  acid  neutralized  by  ammonia,  and  kept  the  sulphuric 
acid  which  was  liberated  by  the  electrolysis,  saturated  with 
metal  by  means  of  oxide  of  nickel  placed  in  the  liquid,  or 
neutralized  it  by  occasionally  adding  ammonia.  When  the 
oxide  is  employed  for  replenishing,  the  liquid  remains  of  the 
same  degree  of  concentration  ;  but  with  ammonia,  it  depo- 
sits clear  green  crystals  of  double  sulphate  of  nickel  and 
ammonium ;  these  are  very  slightly  soluble  in  water  alone, 
but  more  freely  in  that  containing  ammonia.  The  de- 
posited nickel  is  brilliantly  white,  and  may  be  formed  into 
bars,  &c.,  by  electrolysis,  by  having  proper  moulds  to  receive 
it ;  the  bars  possess  magnetic  polarity.  The  solution  of 
double  sulphate  of  nickel  and  ammonium,  whether  containing 
free  ammonia  or  not,  yields  metal  by  electrolysis  (Becquerel, 
'  Chemical  News/  vol.  vi.  p.  126). 

Bottger  states  that  he  has  tried  many  nickel  solutions,  but 
the  best  was  made  by  adding  to  dry  crystals  of  protosulphate 
of  nickel,  as  much  liquid  ammonia  as  was  necessary  to  dis- 
solve them.  The  dark  blue  fluid  was  then  ready  to  use  by 
the  battery  process  ('  Pharmaceutical  Journal/  vol.  iii. 
P-  358). 


238  The  A  rt  of  Electro-Metallurgy. 

M.  Nagel  adds  one  part  of  aqueous  ammonia  to  thirty 
parts  of  water,  then  dissolves  in  it  two  parts  of  crystals  of 
sulphate  of  nickel,  and  adds  six  parts  of  aqueous  ammonia 
of  sp.  gr.  -909.  He  uses  the  solution  at  a  temperature  of 
about  100°  Fahr.  with  a  platinum  anode,  and  a  moderate 
current. 

Another  solution  is  formed  as  follows: — Take  150  parts 
of  water,  add  twelve  and  a  half  of  nitric  acid,  five  of  chloride 
or  sulphate  of  ammonium,  five  of  nitrate  of  ammonium, 
heat  the  mixture  to  80  C.,  and  saturate  it  with  freshly  pre- 
cipitated hydrate  of  nickel,  made  by  precipitating  a  solution 
of  chloride  or  sulphate  of  nickel,  by  one  of  caustic  potash 
or  soda ;  cool  the  mixture,  add  twenty-five  parts  of  aqueous 
ammonia,  dilute  the  whole  with  water  to  250  parts,  dissolve 
in  it  five  parts  of  carbonate  of  ammonium,  filter  the  liquid 
and  use  it  at  a  temperature  of  50  C.  ('  Chemical  Society's 
Journal/  vol.  xii.  p.  928). 

Another  solution  is  composed  of  100  parts  of  sulphate 
of  nickel,  fifty-three  of  tartaric  acid  (dissolved  in  water), 
and  fourteen  of  caustic  potash  added:  it  is  said  to  yield  a 
deposit  of  very  great  beauty,  having  a  bright  silver  lustre, 
without  scratch-brushing. 

According  to  Roseleur,  nickel  may  be  deposited  as  a  dull 
grey  metal,  from  a  solution  made  by  dissolving  nitrate  of 
nickel  in  its  own  weight  of  aqueous  ammonia,  and  diluting 
the  mixture  with  twenty  or  thirty  times  its  volume  of  aqueous 
bisulphite  of  soda  solution  of  sp.  gr.  i'i99- 

Thomas  and  Tilley,  according  to  their  patent  of  Dec.  26, 
1854,  precipitate  a  solution  of  chloride  of  nickel  with  ferro- 
cyanide  of  potassium,  and  dissolve  the  washed  precipitate 
in  a  solution  of  cyanide  of  potassium,  to  form  a  depositing 
liquid. 

Management  of  nickel  plating  solutions. — The  solutions 
are  generally  contained  in  vats  of  wood,  lined  with  asphal- 
tum  (see  p.  313).  As  metallic  nickel  is  much  like  cast  iron, 
and  cannot  be  rolled,  the  anodes  are  composed  of  plates  of 


Management  of  Nickel- Plating  Solutions.      239 

the  cast  metal,  usually  about  1 2  inches  deep,  9  inches  wide, 
and  half  an  inch  or  more  in  thickness ;  and  should  have 
a  much  larger  surface  facing  the  articles,  than  that  of  the 
articles  themselves.  Cast  nickel  contains  a  variable  propor- 
tion of  copper,  carbon,  and  silicon ;  and  when  it  dissolves, 
the  carbon  and  silicon  are  thrown  out  upon  the  surface  in 
the  form  of  a  black  powder,  which  falls  to  the  bottom ;  the 
copper  dissolves  and  is  deposited.  If  plates  of  nickel  can- 
not be  obtained,  fragments  of  metallic  nickel  should  be  sus- 
pended in  baskets  of  platinum-wire  gauze,  but  this  is  not  a 
very  practical  plan,  because  the  current  becomes  impeded 
by  the  impurities  ;  or  a  quantity  of  freshly  precipitated 
hydrated  oxide  of  nickel  in  a  wet  state  should  be  added  to 
the  solution,  and  the  liquid  stirred  up  each  evening. 

Nickel  solutions  are  less  easy  to  manage  than  those  of 
silver.  Some  of  those  employed,  contain  a  large  quantity 
of  the  double  salt,  others  contain  about  four  ounces  per 
gallon.  The  chief  point  to  be  attended  to,  is  to  keep  the 
solution  neutral  or  slightly  alkaline ;  a  few  operators,  how- 
ever, prefer  a  slight  degree  of  acidity.  They  should  be 
frequently  tested  with  neutral  tint  litmus-paper ;  and  am- 
monia should  be  added  if  necessary.  It  is  also  desirable 
to  employ  a  much  larger  surface  of  anode  than  that  of 
the  articles,  and  to  keep  the  anodes  in  the  liquid  whilst 
the  current  is  not  passing  ;  by  these  means  liberation  of 
much  free  acid  is  avoided.  The  current  should  also  be 
maintained  very  uniform,  and  the  articles  kept  in  motion. 
During  the  electrolysis,  more  or  less  hydrogen  is  usually 
evolved  at  the  cathode,  but  this  of  course  depends  upon  the 
composition  of  the  solution,  and  the  '  density'  of  the  current ; 
in  consequence  of  this,  it  is  difficult  to  obtain  thick  deposits, 
the  hydrogen  is  set  free  in  the  metal,  and  causes  it  to  split 
off  in  films.  The  articles  to  be  coated  should  be  very  clean, 
and  also  free  from  scratches ;  the  latter  cause  an  irregular 
deposit.  A  current  from  one  to  three  cells  of  large  surface 
is  usually  sufficient. 


240  The  A  rt  of  Electro-Metallurgy. 

Properties,  uses,  6°r.,  of  electro -deposited  nickel. — Electro- 
deposited  nickel  is  hard,  too  hard  to  be  burnished,  and 
therefore  resists  rough  usage,  and  is  very  much  more  durable 
than  an  equal  thickness  of  silver,  but  the  deposits  are  usually 
very  thin.  '  Laminae  of  electro-deposited  nickel  sometimes 
contain  forty  times  their  volume  of  hydrogen  '(MM.  L.  Troost 
and  P.  Hautefeuille  ('  Chemical  News,'  vol.  xxxi.  p.  196). 

Nickel  has  sometimes  a  dull  appearance  when  deposited, 
but  in  consequence  of  its  hardness  a  high  degree  of  polish 
may  be  imparted  to  it  by  mechanical  means.  It  must  not 
be  ' scratch-brushed '  with  brass  brushes,  because  they 
make  it  yellow.  Its  colour  when  polished,  is  more  blue 
than  that  of  silver,  and  changes  to  a  slightly  yellowish 
tint  by  lapse  of  time.  It  does  not  readily  oxidise  in  the  air, 
even  when  wet ;  but  it  is  easily  corroded  by  acids.  Whilst 
silver  is  rapidly  blackened  by  sulphuretted  hydrogen,  nickel 
is  not  affected.  In  consequence  of  its  hardness,  and  in- 
difference to  sulphuretted  gases,  it  retains  its  polish  a  very 
long  time.  Nickel  should  not  be  employed  for  coating  the 
interior  of  cooking  utensils,  because  of  its  being  corroded  by 
acids,  and  having  poisonous  properties.  Although  metallic 
nickel  is  much  less  expensive  than  silver,  the  cost  of  nickel- 
plating  is  not  proportionately  less,  because  the  value  of  the 
metal  is  not  the  greatest  part  of  the  expense.  In  America, 
spoons  and  forks  are  said  to  be  coated  at  twenty-five  cents 
per  dozen,  and  saddlery  trimmings  at  thirty  cents.  It  is 
very  useful  for  harness  furniture,  carriage  fittings,  scales  and 
weights,  points  of  lightning  conductors,  and  for  many  other 
purposes,  and  the  electro-deposition  of  it  has  greatly  ex- 
tended. There  are  establishments  in  which  it  is  carried  on, 
in  Birmingham,  Sheffield,  London,  New  York,  Philadephia, 
and  other  places ;  at  the  Star  Nickel-plating  works,  Phila- 
delphia, they  operate  in  accordance  with  the  patents  of 
Dr.  Isaac  Adams. 

Estimation  of  nickel  by  means  of  the  battery. — A  solution 
containing  one  gramme  of  the  pure  double  sulphate  of  nickel 


Salts  of  Cobalt.  241 

and  ammonium  was  analysed;  with  a  current  from  two 
Grove's  cells,  it  required  two  hours  for  its  reduction,  and 
yielded  in  three  experiments  1479,  I4'7^,  and  1477  Per 
cent  of  nickel;  the  theoretical  amount  is  1472  per  cent. 
Samples  of  the  commercial  sulphate,  gave  2  2 '07,  21*87,  21*84, 
2 1 '43,  and  22*05  per  cent ;  theory  required  20*71  per  cent. 
The  double  sulphate  of  nickel  and  potassium  gave  13*33, 
13*37,  and  i3'24  per  cent;  theory  required  13*29  per  cent. 
With  a  larger  amount  of  the  same  salt,  13*24  per  cent  was  ob- 
tained. The  double  phosphate  of  nickel  and  potassium, 
yielded  13*27  per  cent,  theory  requiring  13*29.  The 
metallic  deposits  were  washed  with  alcohol,  and  cautiously 
dried  (I.  M.  Merrick,  '  Chemical  News/  vol.  xxiv.  pp.  100, 

172). 

17.  Cobalt. — Elec.   chem.  eqt.  =  59  =  29-6.      Metallic 

cobalt,  especially  in  the  form  of  bars  or  plates,  can  rarely  be 
obtained,  because  it  is  not  only  extremely  difficult  to  melt, 
but  there  is  very  great  loss  by  oxidation  in  the  process.  The 
commonest  salts  of  cobalt,  are  the  oxide,  nitrate,  and  chloride. 
The  oxide  may  best  be  purchased :  there  are  two  varieties 
of  it,  one  a  black  powder  containing  more  oxygen,  and  the 
other  brownish  black,  and  containing  less,  having  been  more 
strongly  heated.  The  chloride  may  be  made,  by  digesting 
the  oxide  in  hot  and  strong  hydrochloric  acid,  and  evapo- 
rating the  deep  blue  liquid ;  it  yields  purplish  red  crystals, 
freely  soluble  in  water.  The  nitrate  is  prepared  by  digest- 
ing the  oxide  in  nitric  acid,  and  evaporating  the  solution  ; 
it  is  in  the  form  of  deliquescent  red  crystals  ;  freely  soluble 
in  water. 

According  to  Becquerel,  copper  immersed  in  a  solution 
of  double  chloride  of  cobalt  and  sodium,  acquires  a  coating  of 
cobalt  ('The  Chemist/  vol.  v.  p.  408).  Magnesium  slowly 
deposits  hydrated  oxide  of  cobalt  from  a  solution  of  the 
sulphate  (Commaille,  'Chemical  News,'  vol.  xiv.  p.  188). 
But  from  slightly  acid  solutions  of  protoxide  of  cobalt,  mag- 


242  The  A  rt  of  Electro-Metallurgy, 

nesium  deposits  metallic  cobalt  and  hydrogen  gas  (Roussin, 
'Chemical  News,'  vol.  xiv.  p.  27). 

Electrolysis  of  salts  of  cobalt. — Very  little  has  been  done 
to  ascertain  the  behaviour  of  these  salts  by  electrolysis. 
I  electrolysed  the  fluoride  dissolved  in  pure  dilute  hydro- 
fluoric acid,  with  a  current  from  a  single  Smee's  element, 
an  anode  of  cobalt,  and  a  cathode  of  copper.  The  con- 
duction was  very  sparing,  and  only  a  film  of  black  powder 
appeared  on  the  cathode  in  twelve  hours.  According  to 
Smee,  this  metal  may  be  reduced  from  its  chloride  (to  which 
an  excess  of  ammonia  has  been  added)  by  using  a  cobalt 
anode,  a  series  of  battery  cells,  and  a  cathode  of  copper. 
The  reduced  metal  is  white,  but  is  not  deposited  freely. 
It  may  also  be  reduced  from  a  solution,  formed  by  digesting 
oxide  of  cobalt  in  cyanide  of  potassium ;  but  only  in  small 
quantity,  hydrogen  being  freely  evolved. 

W.  Wernicke  says  that  the  hydrated  oxide,  dissolved  in 
water  containing  cream  of  tartar  and  a  little  caustic  soda, 
yields,  when  electrolysed  with  electrodes  of  platinum,  solid 
hydrated  peroxide  of  cobalt  upon  the  anode.  The  deposit 
exhibits  magnificent  interference  colours,  which  are  valuable 
for  the  purposes  of  metallo-chromy,  and  are  readily  produced, 
and  permanent  ('  Chemical  News/  vol.  xxii.  p.  240 ;  *  Journal 
of  the  Chemical  Society/  vol.  ix.  p.  307). 

Deposition  of  cobalt  by  contact  with  another  metal. — C. 
Mene  deposits  the  metal  upon  articles  of  zinc,  lead,  iron, 
brass,  or  copper,  by  immersing  them  in  contact  with  zinc, 
in  a  boiling  hot  and  neutral  solution  of  chloride  of  zinc, 
containing  fragments  of  metallic  cobalt  (*  Chemical  News/ 
vol.  xxv.  p.  214).  According  to  Stolba,  salts  of  cobalt  treated 
in  a  similar  manner  to  those  of  nickel  (see  p.  234),  yield  a 
metallic  deposit  of  a  steel-grey  colour,  less  lustrous  than  nickel, 
and  more  liable  to  tarnish. 

Deposition  of  cobalt  by  separate  current  process. — Accord- 
ing to  Becquerel,  a  concentrated  solution  of  the  chloride, 
with  its  excess  of  acid  neutralised  by  addition  of  caustic 


Deposition  of  Cobalt  by  Separate  Current.      243 

potash  or  ammonia,  and  electrolysed  by  a  very  weak  current, 
deposits  its  metal  in  coherent  tubercles,  or  in  uniform 
layers,  according  to  the  strength  of  the  current.  The  de- 
posited metal  is  brilliantly  white,  hard,  and  brittle,  and  may 
be  obtained  in  cylinders,  bars,  and  medals,  by  using  proper 
moulds  to  receive  it.  The  deposited  rods  are  magnetic,  and 
possess  polarity.  With  an  anode  of  cobalt,  it  is  unnecessary 
to  alter  the  solution  after  its  first  preparation.  Part  of  the 
chlorine  of  the  solution  is  disengaged  during  the  electrolysis. 
If  the  liquid  contains  iron,  the  greater  portion  of  it  is  not 
deposited  with  cobalt  ('  Chemical  News/  vol.  vi.  p.  126). 

To  deposit  the  metal,  dissolve  five  ounces  of  the  dry 
chloride  in  a  gallon  of  distilled  water,  and  make  the  solution 
slightly  alkaline  with  ammonia.  Pass  the  current  through 
the  liquid,  either  by  using  a  plate  of  cobalt  as  anode,  or  a 
bar  of  gas-carbon  in  contact  with  a  heap  of  fragments  of 
cobalt  contained  in  a  gutta-percha  basket.  From  two  to 
five  Smee's  cells  are  required.  The  solution  must  be  kept 
slightly  alkaline  ('Telegraphic  Journal/  vol.  ii.,  p.  246). 
'Laminae  of  electro-deposited  cobalt,  sometimes  contain 
thirty-five  times  their  volume  of  hydrogen  '  (Troost  and 
Hautefeuille,  *  Chemical  News/  vol.  31,  p.  196). 

1 8.  Iron. — Elec.-chem.    eqt.  =  ^—  =  28.      A    plate  of 

2 

iron  15  centimetres  square,  and  two  millimetres  thick,  was 
deposited  on  copper  by  Herr  Bockbushmann,  in  the  year 
1846.  In  1857,  M.  Feuquieres  exhibited  specimens  of 
electro-deposited  iron  at  the  Paris  Exhibition.  In  1858, 
M.  Gamier  patented  his  process,  termed  acierage  (steeling), 
for  protecting  the  surfaces  of  engraved  copper  plates ;  and 
in  the  same  year,  Klein  produced  his  beautiful  specimens  of 
electro-deposited  iron. 

Iron  is  a  very  impure  metal,  and  liable  to  contain  carbon, 
silicon,  &c. ;  its  least  impure  form  is  wrought  iron.  Its 
commonest  salts  are  the  peroxide,  (called  also  sesqui-oxide 
of  iron,  jewellers'  rouge,  &c.);  the  protosulphate,  (called 

R  2 


244  The  Art  of  Electro-Metallurgy. 

also  green  vitriol) ;  the  carbonate ;  the  protochloride ;  and 
the  perchloride.  The  peroxide  may  be  readily  obtained, 
by  adding  some  nitric  acid  to  a  solution  of  green  vitriol, 
boiling  the  mixture,  adding  an  excess  of  aqueous  ammonia, 
and  washing  and  drying  the  precipitate ;  it  is  a  brick-red 
powder.  The  protosulphate  is  most  conveniently  purchased, 
it  is  very  cheap  ;  it  may  however  be  prepared,  by  digest- 
ing fine  iron  wire  in  partly  diluted  sulphuric  acid,  in  a  nearly 
filled  and  covered  glass  vessel,  until  no  more  will  dissolve, 
and  then  evaporating  the  solution,  as  much  as  possible  out 
of  contact  with  air;  it  is  a  green  crystalline  salt,  freely  soluble 
in  water.  The  protochloride  may  be  similarly  prepared, 
by  using  hydrochloric  acid  instead  of  sulphuric;  it  is  also 
of  a  green  colour,  and  very  soluble.  The  solutions  of  all 
protosalts  of  iron,  rapidly  absorb  oxygen  from  the  atmo- 
sphere, and  become  persalts.  The  perchloride  is  made,  by 
adding  some  nitric  acid  to  a  solution  of  the  protochloride, 
and  then  boiling  the  mixture  down  to  the  crystallising  point 
in  a  wide  porcelain  dish ;  it  is  a  brick-red  salt,  very  soluble 
in  water,  and  liable  to  produce  a  cloudy  solution. 

Deposition  of  iron  by  simple  immersion  (see  p.  79). — Mag- 
nesium deposits  from  a  neutral  solution  of  ferrous  sulphate, 
hydrated  ferrous  oxide,  but  from  an  acidified  solution  it 
deposits  metallic  iron  (Commaille,  *  Chemical  News/  vol. 
xiv.  p.  1 8 8).  From  slightly  acid  solutions  of  proto  and 
sesqui  salts  of  the  metal,  magnesium  deposits  pure  iron  and 
hydrogen  gas  (Roussin,  'Chemical  News/ vol.  xiv.  p.  27). 
Gold  in  contact  with  iron,  and  immersed  in  cold  or  boiling, 
acid  or  neutral,  solutions  of  salts  of  iron,  does,  not  receive 
a  metallic  deposit  (Raoult,  '  Chemical  News/  vol.  xxvi. 
p.  240,  vol.  xxvii,  p.  59  ;  'Journal  of  Chemical  Society/ vol. 
xi.  p.  465), 

Electrolysis  of  salts  of  iron. — Iron  maybe  reduced  from  a 
solution  of  its  protosulphate  (green  copperas),  or  from  its 
protochloride,  which  is  preferable.  I  have  deposited  it  in 
the  state  of  reguline  white  metal,  by  passing  a  current  of 


Electrolysis  of  Salts  of  Iron.  245 

considerable  intensity  (from  fifteen  or  twenty  Smee's  cells), 
for  one  hour,  through  an  anode  of  iron  immersed  in  a  satu- 
rated aqueous  solution  of  salammoniac ;  its  appearance  when 
deposited  from  this  liquid  is  rather  white,  very  similar  to 
that  of  freshly  broken  cast  iron.  By  similar  means  it  may 
also  be  deposited,  using  a  saturated  solution,  either  of  car- 
bonate of  ammonium,  acetate  of  ammonium,  or  acetate  of 
potassium.  Good  metal  may  also  be  deposited  from  a  satu- 
rated aqueous  solution,  of  a  mixture  of  two  parts  of  protosul- 
phate  of  iron  and  one  of  salammoniac.  I  have  deposited 
it  from  an  aqueous  solution  of  ferrate  of  potassium,  formed, 
either  by  igniting  peroxide  of  iron  very  strongly  for  some 
minutes  with  caustic  potash  and  saltpetre,  and  dissolving 
the  product  in  water ;  or  by  making  a  very  strong  solution 
of  caustic  potash,  immersing  in  it  a  large  iron  or(  steel  anode, 
and  a  small  copper  or  platinum  cathode,  and  passing  a  strong 
current  from  fifteen  or  twenty  Smee's  cells  through  it,  until 
it  acquires  a  deep  amethystine  or  purple  colour  ;  by  that 
time,  the  cathode  will  have  obtained  a  coating  of  iron,  which 
will  be  in  the  state  of  a  dark  powder  if  the  power  has  been 
too  great,  or  it  will  have  the  appearance  of  white  cast  iron 
(or  intermediate  between  that  and  the  appearance  of  reguline 
deposited  zinc),  if  the  power  has  been  sufficiently  weak. 
The  solution  rapidly  decomposes,  becomes  colourless,  and 
deposits  all  its  metal  in  the  state  of  peroxide  at  the  bottom 
of  the  vessel.  Iron  may  be  very  easily  deposited  from  its 
sulphate  thus  :  dissolve  a  little  of  the  salt  in  water,  and  add 
a  few  drops  of  sulphuric  acid  to  the  solution  ;  one  Smee's 
cell  may  be  used  to  deposit  it  upon  copper  or  brass.  The 
metal  in  its  pure  coherent  state,  has  a  very  bright  and  beauti- 
ful silvery  appearance.  An  aqueous  solution  of  cyanide  of 
potassium  is  a  very  bad  conductor  with  an  iron  anode,  even 
if  it  be  maintained  hot.  Solutions  of  persalts  of  iron  yield 
no  metallic  deposit,  but  are  reduced  to  protosalts,  by  the 
passage  of  an  electric  current  through  them. 

Walenn  deposited  reguline,  white,  silvery-looking  iron, 


246  The  A  rt  of  Electro-Metallurgy. 

(attended  by  the  evolution  of  much  hydrogen)  from  a  cold 
and  slightly  acid  solution,  composed  of  one  part  of  crystal- 
lised ferrous  sulphate,  dissolved  in  five  of  water ;  employing 
a  current  from  three  Smee's  elements  of  about  ten  times  the 
amount  of  surface  as  that  of  the  electrodes.  The  addition 
of  sulphate  of  ammonium  increased  the  conducting  power, 
and  formed  a  very  good  depositing  solution  ('  Chemical 
News/  vol.  xvii.  p.  170). 

One  of  the  best  liquids  for  depositing  iron,  is  that  of 
M.  Klein,  prepared  as  follows  : — Precipitate  a  solution  of 
ferrous  sulphate  (green  vitriol)  by  means  of  carbonate  of 
ammonium,  and  dissolve  the  washed  precipitate  in  sul- 
phuric acid,  taking  care  to  avoid  any  free  acid.  Use  the 
bath  as  concentrated  as  possible.  Good  reguline  metal 
may  be  obtained  fron  it,  by  means  of  a  current  from 
four  weak  Meidinger's  cells,  with  an  anode  of  iron  and  a 
cathode  of  copper.  It  is  highly  important  to  prevent  the 
bath  becoming  acid  by  the  working,  &c.,  and  this  is  effected 
by  using  an  anode  eight  times  the  size  of  the  receiving  sur- 
faces, and  by  attaching  a  plate  of  copper  or  platinum  to 
it,  so  that  the  two  form  a  voltaic  pair  in  the  liquid,  and 
thus  cause  the  iron  to  dissolve  whilst  the  battery  current  is 
not  passing.  The  metal  obtained  from  it,  is  as  hard  as  tem- 
pered steel,  and  very  brittle,  but  after  annealing,  it  is  malle- 
able, and  may  be  engraved  as  easily  as  soft  steel.  He  also 
employs  a  bath,  composed  of  the  double  sulphate  of  iron 
and  magnesium,  of  sp.  gr.  1*155  ;  the  liquid  must  be  neutral, 
and  the  electric  current  very  feeble.  The  iron  obtained 
from  it  has  a  sp.  gr.  cf  8-139  ;  it  occludes  thirteen  times 
its  volume  of  hydrogen,  and  possesses  a  higher  electric  con- 
ductivity  than  any  commercial  iron  ;  it  does  not  warp  or 
contract  when  heated,  but  slightly  expands,  and  is  not 
porous  ('  Chemical  News,'  vol.  xviii.  p.  133,  and  vol.  xxxi. 
p.  137  ;  'Telegraphic  Journal/  vol.  ii.  p.  128). 

'  Copying  engraved  metal  plates  with  copper  and  giving  them 
a  surface  of  iron. — If  the  engraved  plate  is  of  steel,  boil  it  one 


Facing  Copper  Plates  with  Iron. 

hour  in  caustic  potash  solution .  Brush  and  wash  it  well.  Wipe 
it  dry  with  a  rag,  and  then  with  one  moistened  with  benzine. 

'  Melt  six  pounds  of  the  best  gutta-percha  very  slowly 
indeed,  the  gum  being  previously  cut  up  into  very  small 
pieces.  Add  to  it  three  pounds  of  refined  lard,  and 
thoroughly  incorporate  the  mixture.  Pour  the  melted  sub- 
stance upon  the  centre  of  the  plate.  Allow  it  to  stand  twelve 
hours,  and  then  take  the  copy  off. 

'  Phosphorus  solution. — Dissolve  a  fragment  of  phosphorus 
half  an  inch  in  diameter,  in  one  teaspoonful  of  bisulphide 
of  carbon,  add  a  similar  measure  of  pure  benzine,  three  drops 
of  sulphuric  ether,  and  half  a  pint  of  spirits  of  wine.  Wash 
the  mould  twice  with  this  solution,  allowing  it  to  dry  each 
time. 

'  Silver  solution. — Dissolve  one-sixth  of  an  ounce  of  nitrate 
of  silver,  in  a  mixture  of  half  a  pint  of  strong  alcohol,  and 
half  a  teaspoonful  of  acetic  acid,  wash  the  mould  once  with 
this  liquid,  and  allow  it  to  dry. 

'  Copper  solutions. — Dissolve  fifty-six  pounds  of  sulphate 
of  copper,  in  nineteen  gallons  of  water,  and  add  one  gallon 
of  oil  of  vitriol.  Deposit  a  plate  of  copper  upon  the  mould 
in  this  solution. 

'  Iron  solution. — To  coat  the  copper  plate  with  a  surface 
of  iron,  dissolve  fifty-six  pounds  of  carbonate  of  ammo- 
nium, in  thirty-five  gallons  of  water.  Dissolve  iron  into  the 
liquid,  by  means  of  a  clean  anode  of  charcoal  iron,  and  a 
current  from  a  battery.  Clean  the  anode  frequently,  and 
add  one  pound  of  carbonate  of  ammonium  once  a  week.  The 
copper  plate  before  receiving  the  deposit,  should  be  cleansed 
with  pure  benzine,  then  with  caustic  potash,  and  thoroughly 
with  water.  Immerse  the  cathode  in  the  iron  solution  for 
four  minutes,  take  it  out,  wash,  scrub,  re-place  in  the  vat, 
remove  and  brush  it  every  five  minutes,  until  there  is  a  suffi- 
cient deposit.  Then  wash  it  thoroughly,  well  dry,  oil  and  rub 
it,  and  clean  with  benzine.  If  it  is  not  to  be  used  at  once, 
coat  it  with  a  film  of  wax. 


248  The  A  rt  of  Electro-Metallurgy. 

Meidinger  coats  engraved  copper  plates  with  iron,  in  a 
solution  of  sulphate  of  iron  and  chloride  of  ammonium  ; 
and  the  plates  serve  for  as  many  as  from  5,000  to  15,000 
impressions  (Wagner's  'Technology,'  p.  116). 

Management  of  iron  depositing  solutions. — Hydrogen  is 
very  apt  to  be  evolved  at  the  cathode  in  solutions  of  iron. 
Such  liquids  also  soon  spoil  for  the  purpose  of  electro 
deposition,  because  they  absorb  oxygen  from  the  air,  and 
become  persalts ;  and  the  energy  of  the  electric  current, 
instead  of  being  expended  in  liberating  metal,  is  consumed 
in  de-oxidising  the  solution  at  the  surface  of  the  articles. 
Solutions  of  ferrous  chloride  become  turbid,  and  continually 
deposit  a  slimy  precipitate  upon  the  electrodes.  Iron  solu- 
tions should,  therefore,  be  covered  as  much  as  possible  from 
the  air,  but  this  cannot  usually  be  conveniently  done.  Klein 
adopted  the  expedient,  of  adding  glycerine  to  the  liquid,  in 
order  to  retard  the  change.  His  solution  keeps  pretty  clear, 
but  has  upon  its  surface  a  slimy  foam,  which  sometimes  falls 
upon  the  articles. 

When  iron  is  deposited  from  some  liquids — for  instance, 
one  composed  of  the,  double  chloride  of  iron  and  ammonium, 
to  which  is  added  a  small  quantity  of  glycerine, — after  the 
deposit  has  attained  a  certain  thickness,  its  surface  cracks, 
and  brittle  spangles  are  detached  and  fall  to  the  bottom. 
Deposits  of  iron  should  be  immersed  in  boiling  water,  in 
order  to  remove  dissolved  salts,  and  prevent  rusting. 

Properties  and  uses  of  electro-d 'posited  iron. — Voltaic  iron 
receives  magnetism  like  soft  steel.  According  to  W.  Beetz, 
iron  electro-deposited  from  a  solution  containing  salam- 
moniac,  is,  in  a  very  eminent  degree,  capable  of  permanent 
magnetism;  and  if  deposited  under  the  influence  of  power- 
ful magnets,  is  itself  strongly  magnetic.  The  salammoniac 
is  essential  to  the  formation  of  good  electrolytic  magnets 
('Telegraphic  Journal/  vol.  ii.  p.  399). 

The  earlier  formed  deposits  of  iron,  were  full  of  holes,  and 
quite  spongy  in  texture,  in  consequence  of  bubbles  of  hydro  - 


Properties  of  Electro-deposited  Iron.  249 

gen,  but  by  keeping  the  solutions  free  from  uncombined  acid, 
and  employing  a  sufficiently  feeble  current,  that  defect  has 
been  almost  entirely  obviated.  Iron  also,  in  common  with 
many  other  metals  in  the  act  of  electro-deposition,  occludes 
hydrogen  (see  p.  97).  According  to  R.  Leng  ('  Chemical 
News,'  vol.  xxi.  p.  179),  it  contains  185  times  its  volume, 
chiefly  in  the  first  layers  deposited.  According  to  Troost  and 
Hautefeuille  ('  Chemical  News,'  vol.  xxxi.  p.  196),  it  some- 
times contains  as  much  as  260  times  its  bulk.  L.  Cailletet 
states,  that  by  decomposing  by  an  electric  current,  a  neutral 
solution  of  ferrous  chloride,  to  which  salammoniac  has  been 
added,  the  iron  has  been  deposited  in  the  form  of  mammil- 
lary  masses,  brittle,  brilliant,  and  hard  enough  to  scratch 
glass ;  and  when  the  deposit  is  plunged  into  water,  or  other 
liquid,  numerous  bubbles  of  pure  hydrogen  are  given  off. 
One  volume  of  iron  absorbs  about  240  volumes  of  hydrogen, 
and  by  contact  with  a  flame,  the  gas  ignites,  surrounding 
the  metal  with  a  pale  colour  ('  Chemical  News,'  vol.  xxxi. 
p.  119  ;  'Journal  of  the  Chemical  Society,'  vol.  xiii.  p.  425). 
The  advantages  of  facing  printing-type,  engraved  copper 
plates,  those  used  for  printing  bank-notes,  &c.  with  iron,  are 
very  considerable.  The  iron  being  very  much  harder  than 
the  other  metals,  is  so  much  the  more  durable,  and  is  not 
so  readily  injured  by  knots  in  the  paper,  or  by  other  sub- 
stances accidentally  present.  It  also  takes  the  ink  readily, 
and,  unlike  copper,  is  not  injured  by  ink  containing  vermi- 
lion; also,  when  the  iron  facing  has  lost  its  sharpness  of  impres- 
sion, it  may  be  dissolved  off  by  means  of  dilute  sulphuric  acid, 
without  affecting  the  copper,  and  a  new  coating  may  be  put 
on,  possessing  all  the  original  sharpness ;  and  this  may  be 
repeated  a  very  gieat  number  of  times. 

19.  Manganese. — Elec.-chem.  eqt.=  51  =  9-16.       Very 

6 

few  investigations  have  yet  been  made,  in  the  electro- deposi- 
tion of  the  more  intractable  metals,  manganese,  chromium, 
uranium,  tungsten,  molybdenum,  vanadium,  &c.  Junot,  in 


250  The  A  rt  of  Electro-Metallurgy. 

December  1852,  took  out  a  patent  for  'preparing  silicium, 
titanium,  tungsten,  chromium,  and  molybdenum,  by  causing 
them  to  be  deposited  from  their  solutions,  by  means  of 
electric  currents,  upon  metals  and  other  substances  ; '  but 
nothing  has  since  been  heard  of  the  working  of  this 
patent. 

The  commonest  salts  of  manganese,  are  the  black  oxide, 
chloride,  and  carbonate.  The  black  oxide  (pyrolusite),  is 
found  abundantly  as  a  mineral;  contaminated  however 
with  iron  and  various  earthy  matters.  The  chloride  may  be 
formed  in  an  impure  state,  by  digesting  the  black  oxide  in 
hot  and  strong  hydrochloric  acid,  and  evaporating  the  solu- 
tion ;  or  pure,  by  saturating  dilute  hydrochloric  acid  with 
the  carbonate  ;  using  pure  materials.  The  sulphate  may  be 
formed  by  similar  means,  using  however  boiling  hot  dilute 
sulphuric  acid.  The  chloride  and  sulphate  are  pink  salts, 
freely  soluble  in  water. 

Deposition  of  manganese  by  simple  immersion. — Manganese 
is  deposited,  by  the  simple  immersion  of  sodium-amalgam, 
in  an  acidulated  solution  of  a  salt  of  manganese,  it  then 
alloys  with  the  mercury  (Roussin,  'Chemical  News,'  vol. 
xiv.  p.  27).  Giles  deposited  manganese  upon  mercury,  by 
simple  immersion  of  an  amalgam  of  sodium  in  a  saturated 
solution  of  proto-chloride  of  manganese  ('Philosophical 
Magazine/4th  series,  vol.  xxiv.p.  328).  According  to  Phipson, 
magnesium  deposits  manganese  as  a  black  powder,  from  a 
neutral  solution  of  a  proto-salt  of  that  metal.  ('  Proceedings 
of  the  Royal  Society,'  1864,  vol.  xiii.  p.  217  ;  *  Chemical 
News/  vol.  ix.  p.  219).  Magnesium  deposits  hydrated  man- 
ganous  oxide  from  a  neutral  solution  of  manganous  sulphate, 
but  from  the  same  solution  acidified,  it  deposits  metallic 
manganese  (Commaille,  'Chemical  News,'  vol.  xiv.  p.  188). 

Electrolysis  of  salts  of  manganese. — Bunsen  filled  a  porous 
cell,  with  a  hot  and  saturated  aqueous  solution  of  chloride 
of  manganese,  placed  it  in  a  charcoal  crucible  containing 
hydrochloric  acid  to  the  same  level,  put  the  latter  vessel  in 


Electrolysis  of  Salts  of  Manganese.  251 

a  sand-bath  (to  keep  the  liquids  hot),  immersed  a  platinum 
wire  cathode  in  the  centre  of  the  chloride  solution,  and  con- 
nected the  charcoal  crucible  with  the  positive  pole  of  a  four- 
cell  Bunsen's  battery.  Metallic  manganese  was  separated 
with  the  greatest  facility ;  but  if  the  density  of  the  current 
at  the  cathode  was  reduced,  either  by  enlarging  the  cathode, 
diminishing  the  anode,  or  weakening  the  current ;  or  if  the 
degree  of  concentration  of  the  solution  was  diminished, 
black  manganoso-manganic  oxide  was  obtained.  ('The 
Chemist,'  No.  n,  August  1854,  p.  685  ;  Watts'  'Dictionary 
of  Chemistry,'  vol.  ii.  p.  438). 

I  melted  some  fluoride  of  manganese  in  a  platinum 
crucible,  and  employed  two  spirals  of  platinum  wire  as 
electrodes,  and  a  current  from  six  large  Smee's  cells.  The 
conduction  was  moderate,  and  gas  was  evolved  from  the 
anode.  In  a  few  minutes,  both  the  cathode  and  the  crucible 
became  quite  rotten,  by  the  union  of  the  deposited  man- 
ganese with  the  platinum.  The  anode  was  not  corroded. 
I  also  melted  the  same  salt  in  a  crucible  of  copper,  and 
passed  the  current  by  means  of  a  sheet  platinum  anode, 
and  sheet  copper  cathode,  during  half  an  hour.  The  con- 
duction was  free  ;  abundance  of  gas  was  evolved  from  the 
anode,  but  none  from  the  cathode,  and  it  ceased  on  stop- 
ping the  current.  The  deposit  on  the  cathode  was  black, 
and  did  not  evolve  hydrogen  with  dilute  hydrochloric 
acid,  and  was  therefore  not  metallic  manganese.  The 
crucible  was  much  corroded  at  the  line  of  surface  of  the 
liquid. 

I  also  electrolysed  a  dilute  solution  of  fluoride  of  man- 
ganese, by  a  current  from  six  Grove's  cells,  and  electrodes  of 
platinum.  Much  heat  was  evolved,  gas  was  set  free  at  the 
anode,  and  a  film  of  black  deposit  formed  upon  the  cathode. 
By  similar  treatment  of  a  saturated  solution  of  the  salt,  not 
containing  any  free  hydrofluoric  acid,  a  film  of  purple 
colour  was  instantly  formed  upon  the  anode,  but  it  dissolved 
quickly,  and  did  not  colour  the  liquid.  Gas  came  from  both 


252  The  A  rt  of  Electro-Metallurgy. 

electrodes  freely  ;  the  liquid  also  became  heated.  No  solid 
deposit  was  obtained. 

Salts  of  manganese  yield  peroxide  at  the  anode.  A  so- 
lution composed  of  one  part  of  chloride  of  manganese  and 
eight  of  water,  yields  very  beautiful  alternating  rings  of 
purple-green,  golden  yellow,  and  blue,  surrounded  by  a 
broad  belt  of  golden  yellow.  With  a  solution  composed  of 
one  part  of  acetate  of  manganese  and  fifteen  of  water,  one 
uniform  tint  is  invariably  produced,  first  golden  yellow,  then 
purple,  then  green  (B.  Bottger,  '  PoggendorfFs  Annalen,' 
vol.  1.  p,  45). 

According  to  W.  Wernicke,  solutions  of  acetate  and 
nitrate  of  manganese,  with  a  feeble  current  from  two 
Darnell's  cells,  and  platinum  electrodes,  yield  a  deposit  of 
hydrated  peroxide  of  manganese  upon  the  anode  ('Journal 
of  the  Chemical  Society,'  vol.  ix.  p.  307). 

20.  Chromium.  —  Elec.  chem.  eqt.=  51  _  g.^ 


ordinary  compounds  containing  chromium,  are  the  sesqui- 
oxide,  chromic  acid,  the  two  chromates  of  potash,  and 
chrome-alum,  i.e.  the  double  sulphate  of  chromium  and 
potassium.  The  sesquioxide  is  a  substance  particularly  in- 
soluble in  water  and  acids.  The  other  salts  are  freely 
soluble  in  water,  and  are  more  conveniently  purchased  than 
prepared. 

Deposition  of  chromium  by  simple  immersion.  —  Mag- 
nesium deposits  oxide  of  chromium  from  a  solution  of  a 
salt  of  that  metal  ;  but  sodium  amalgam  shaken  up  with 
an  acid  solution  of  such  a  salt,  becomes  an  amalgam, 
from  which  the  metal  itself  may  be  obtained  as  a  spongy 
mass,  by  distilling  away  the  mercury  in  a  current  of  hy- 
drogen. If  the  amalgam  of  chromium  is  heated  in  the  air, 
the  particles  of  chromium  scintillate  singularly,  and  the 
amalgam  then  suddenly  becomes  incandescent  (Roussin, 
*  Chemical  News,'  vol.  xiv.  p.  27).  Magnesium  precipi- 
tates hydrated  sesquioxide  of  chromium,  from  a  mixed 


Deposition  of  Chromium.  253 

solution  of  chromous  and  chromic  chloride  (Commaille, 
'Chemical  News,'  vol.  xiv.  p.  188).  Vincent  deposited 
chromium  upon  mercury,  by  simple  immersion  of  sodium 
amalgam  in  a  solution  of  chloride-  of  chromium  ;  the  latter 
metal  was  then  obtained  in  a  finely  divided  state,  by  distill- 
ing away  the  mercury  in  a  retort  filled  with  vapour  of 
naphtha  ('Philosophical  Magazine,'  fourth  series,  vol. 
xxiv.  p.  328). 

Deposition  of  chromium  by  separate  current. — Bunsen,  by 
operating  in  a  similar  manner  upon  a  concentrated  solution 
of  chloride  of  chromium,  as  upon  one  of  manganese  (see 
p.  250),  deposited  chromium  readily;  the  deposit  presented 
the  appearance  of  iron,  but  was  less  affected  by  damp  air  ; 
it  resisted  the  action  of  boiling  nitric  acid,  but  dissolved  in 
hydrochloric  or  dilute  sulphuric  acid.  It  was  friable,  and 
presented  a  high  polish  on  the  side  next  the  cathode.  On 
diminishing  the  current,  a  black  powder  was  deposited, 
containing  more  oxygen  in  proportion  as  the  density  of  the 
current  was  lessened ;  adding  protochloride  of  chromium  to 
the  solution  had  a  reverse  effect, — it  caused  metallic  chromium 
to  be  deposited  ('The  Chemist/  No.  n,  August  1854, 
p.  686). 

I  melted  some  acid  chromate  of  potassium,  and  passed 
through  it  the  current  from  five  Smee's  elements,  by  means 
of  electrodes  of  platinum.  A  deposit  slowly  formed  upon 
the  cathode.  I  also  electrolysed  a  strong  solution  of 
fluoride  of  chromium,  containing  some  free  hydrofluoric  acid, 
and  a  little  hydrochloric  acid,  by  a  current  from  six  Grove's 
.cells,  and  platinum  electrodes.  The  liquid  soon  became 
hot;  no  gas  was  evolved  from  the  cathode,  but  chlorine 
and  ozone  were  set  free  at  the  anode,  which  was  not 
corroded. 

21.  Uranium. — Elect-chem.   eqt.  =  Ji^l  =  30.        The 

4 

commonest  salt  of  uranium  is  the  sesquioxide,  which  is  a 
yellow  powder,  insoluble  in  water,  but  soluble  in  several 


254  The  Art  of  Electro-Metallurgy. 

mineral  acids.  The  nitrate,  chloride,  bromide,  and  sulphate 
of  uranium  may  be  formed,  by  digesting  an  excess  of  the 
sesquioxide  in  the  corresponding  diluted  acid,  until  it  is 
saturated,  and  evaporating  the  solution ;  they  are  each  of  a 
pale  yellow  colour,  and  soluble  in  water. 

Magnesium  deposits  golden-coloured  hydrated  sesqui- 
oxide of  uranium,  from  a  solution  of  oxalate  of  uranium 
(Commaille,  'Chemical  News,'  vol.  xiv.  p.  188).  I  fused 
some  fluoride  of  uranium  in  a  platinum  crucible,  and 
added  to  it  some  crystals  of  silicon ;  the  salt  was  not  de- 
composed. 

Electrolysis  of  salts  of  uranium. — I  also  fused  some 
fluoride  of  uranium  in  a  copper  crucible,  and  passed  a 
current  from  six  Smee's  cells  through  it,  by  means  of  a 
platinum  wire  anode,  using  the  crucible  as  a  cathode;  a 
little  gas  was  set  free  at  the  anode,  and  the  crucible  melted. 
A  second  trial  was  made,  using  a  platinum  crucible,  and  two 
spirals  of  platinum  wire  as  electrodes,  and  the  current  con- 
tinued during  one  hour.  Conduction  was  very  free,  much 
gas  was  evolved  from  the  anode,  but  none  from  the  cathode; 
a  bulky  deposit  quickly  formed  upon  the  negative  spiral, 
especially  on  the  side  towards  the  anode.  The  deposit 
weighed  43*66  grains,  and  consisted  of  hard  jet-black  crystals. 
The  anode  was  not  corroded.  In  a  third  trial,  four  Grove's 
cells  were  employed,  and  a  special  apparatus  devised  and 
employed  to  collect  the  evolved  gas,  and  about  five  cubic 
inches  were  obtained.  The  crystals  were  not  metallic  ura- 
nium ;  they  were  insoluble  in  boiling  water,  but  soluble  in 
cold  dilute  hydrofluoric  acid,  without  evolving  gas.  About 
one-fourth  of  the  deposit,  consisted  of  a  fine  crystalline 
powder,  nearly  of  the  colour  of  copper,  but  darker,  and 
was  composed  of  the  crystals,  with  a  film  of  less  reduced 
fluoride  upon  them  ;  they  evolved  gas  in  cold  nitric  acid, 
or  in  hot  dilute  nitric  acid.  They  were  not  fused  by  heat- 
ing alone  to  redness  upon  platinum  foil ;  but  if  caustic 
potash  was  added,  they  oxidised.  I  also  electrolysed  a 


Electrolysis  of  Tungstate  of  Sodium.          255 

fused  mixture  of  the  pure  fluorides  of  uranium  and  potas- 
sium, with  platinum  electrodes ;  the  results  were  very 
similar,  except  that  the  deposit  upon  the  cathode  fell  off  as 
fast  as  it  was  formed  ;  and  the  crystals  had  to  be  extracted 
by  dissolving  the  cooled  saline  mass  in  slightly  diluted  and 
hot  hydrochloric  acid  ;  they  were  very  much  like  those 
of  silicon;  their  form  was  that  of  a  short  pyramid  with  a 
square  base.  The  anode  was  very  slightly  corroded  and 
made  bright  by  the  action ;  and  twenty  cubic  inches  of  gas 
were  collected  from  it. 

I  also  electrolysed  a  strong  aqueous  solution  of  fluoride 
of  uranium,  with  a  current  from  six  Grove's  cells,  and  plati- 
num electrodes.  Much  gas,  having  the  odour  of  ozone,  was 
evolved  from  the  anode,  and  the  liquid  became  hot.  I  then 
added  some  aqueous  hydrofluoric  acid  ;  the  conduction  was 
very  free,  and  abundance  of  gas  evolved  from  each  electrode, 
but  no  solid  deposit  was  formed. 

22.  Tungsten.— Elec.  chem.  eqt.=  i?^-  =  30-66.     The 

6 

only  readily  available  salts  of  this  metal,  are  tungstic  acid, 
and  tungstate  of  sodium  ;  the  former  is  a  yellow  powder, 
insoluble  in  water  and  in  acids ;  the  latter  is  a  colourless 
salt,  soluble  in  water. 

I  fused  some  tungstate  of  sodium  to  a  clear  liquid 
in  a1  porcelain  vessel,  and  electrolysed  it  by  means  of  a 
current  from  five  Smee's  cells,  a  gas -carbon  anode,  and  a 
platinum  wire  cathode.  The  conduction  was  moderately 
free,  gas  was  evolved  from  the  anode,  and  at  the  cathode, 
black  matter  was  set  free,  which  floated,  and  became  diffused 
in  the  liquid,  and  partly  re-dissolved. 

23.  Molybdenum. — Elec. -chem.    eqt.=  —  =  16.    The 

6 

only  common  salts  of  this  metal,  are  molybdic  acid,  sulphide 
of  molybdenum,  and  molybdate  of  ammonium.  Molybdic 
acid  may  be  prepared,  by  digesting  sulphide  of  molybdenum 
in  strong  nitric  acid ;  it  is  a  pale  yellow  powder,  insoluble  in 


256  The  Art  of  Electro-Metallurgy. 

water.  The  sulphide  is  a  mineral  substance,  looking  like 
black-lead,  and  insoluble  in  water.  The  molybdate  of 
ammonium  is  white,  and  sparingly  soluble  in  water. 

Electrolysis  of  molybdic  acid. — I  fused  some  molybdic 
acid  in  a  porcelain  crucible,  and  passed  the  current  from  five 
Smee's  cells  through  it,  by  means  of  a  gas-carbon  anode,  and 
platinum  cathode.  It  conducted  freely.  The  action  was 
rather  strong  at  the  anode,  but  little  gas  was  evolved.  Black 
crystals  quickly  collected  round  the  cathode,  but  no  gas  was 
set  free  with  them  ;  the  entire  liquid  soon  became  full  of 
the  crystals,  which  spread  quickly  to  the  anode.  The  carbon 
was  not  dissolved,  or  disintegrated.  The  cooled  residue 
was  a  solid  black  mass  of  crystals,  which  dissolved  sparingly 
in  water,  and  formed  a  blue  liquid.  In  a  second  experiment, 
using  twelve  large  Smee's  elements,  and  platinum  anode  and 
cathode,  there  was  free  action,  and  much  gas  evolved  ;  and 
the  bluish-black  deposit  quickly  formed  upon  the  cathode. 
Most  of  the  gas  came  from  the  anode.  A  large  quantity  of 
crystalline  needles  (-Jth  to  Jth  of  an  inch  long),  formed  upon 
the  cathode,  and  stood  out  at  right  angles  to  its  surface  in  the 
fused  substance.  The  deposit  imparted  a  transient  green 
colour  to  water. 

Molybdic  acid  dissolved  freely  in  pure  hydrofluoric  acid, 
evolving  a  little  heat.  The  solution  was  electrolysed,  both 
with  a  carbon  and  with  a  platinum  anode.  The  colourless 
liquid  conducted  freely  a  current  from  ten  large  Smee's  cells, 
became  instantly  blue,  and  almost  black,  at  a  platinum  cathode. 
Gas  was  evolved  at  each  electrode,  that  from  the  gas-carbon 
anode  was  the  most  abundant,  and  had  a  slightly  chlorous 
odour.  On  stopping  the  current,  the  deep  blue  film  on  the 
cathode  quickly  dissolved,  and  the  liquid  soon  became 
colourless.  During  the  action,  the  cathode  was  several  times 
removed  from  the  electrolyte,  and  dipped  into  water;  much 
blue  matter  dissolved,  but  the  water  became  nearly  colour- 
less in  half  a  minute,  even  without  stirring,  and  however 
large  the  quantity  of  blue  matter  was,  which  dissolved  in  it. 


Deposition  of  Lead  by  Simple  Immersion.       257 

24.  Vanadium. — Elec.-chem.  eqt.  =  -^-  =  22-8.     The 

only  readily  attainable  compounds  of  this  element,  are 
vanadic  acid,  and  vanadate  of  ammonium.  I  electrolysed 
a  solution  composed  of  vanadic  acid  dissolved  in  pure 
dilute  hydrofluoric  acid,  with  a  gas-carbon  anode  and  plati- 
num cathode,  and  ten  Smee's  cells.  Gas  having  an  odour 
of  ozone  was  evolved  from  the  anode.  I  also  saturated 
dilute  sulphuric  acid  with  pure  vanadate  of  ammonium,  and 
electrolysed  it  with  platinum  electrodes,  and  a  current  from 
four  platinum  and  zinc  elements.  The  conduction  was  very 
sparing  ;  the  solution  became  gradually  of  a  very  intense 
bluish-black  colour  from  action  at  the  cathode,  and  a  jet- 
black  powdery  deposit  of  some  thickness  formed  upon  that 
electrode. 

25.  Lead. — Elec.-chem.  eqt.  =  ^1  =  103-5.  The  com. 

monest  salts  of  lead,  besides  its  three  oxides,  viz.  litharge, 
red-lead,  and  peroxide  of  lead,  are  the  nitrate,  chloride,  car- 
bonate, sulphate,  and  acetate.  All  of  these  may  be  readily 
purchased  in  a  comparatively  pure  state.  The  nitrate  and 
acetate,  are  the  two  common  soluble  salts  of  the  metal ;  thq 
others  may  be  readily  made,  by  dissolving  litharge,  red-lead, 
or  carbonate  of  lead,  in  the  particular  acids,  to  saturation, 
and  evaporating  the  solutions. 

Deposition  of  lead  by  simple  immersion. — (See  also  p.  79.) 
— The  old  experiment  of  producing  a  lead  tree,  by  suspending 
a  spiral  of  zinc  wire  in  a  solution  of  nitrate  or  acetate  of 
lead,  is  well  known.  According  to  A.  Cossa,  aluminium 
slowly  deposits  lead  in  crystals,  from  a  solution  of  plumbic 
nitrate  or  acetate,  and  immediately  from  a  solution  of  the 
chloride.  An  alkaline  solution  of  plumbic  chromate,  is  also  at 
once  decomposed  by  that  metal,  with  separation  of  metallic 
lead,  and  formation  of  chromic  oxide  (Watts'  '  Dictionary  of 
Chemistry,'  vol.  vii.  p.  54).  Magnesium  deposits  lead  and 
oxychloride  of  lead,  together  with  much  hydrogen,  from  a 


258  The  A  rt  of  Electro-Metallurgy. 

neutral  solution  of  plumbic  chloride  (Commaille,  '  Chemical 
News,'  vol.  xiv.  p.  188). 

I  melted  some  plumbic  fluoride  in  a  platinum  crucible, 
and  added  some  crystals  of  boron ;  metallic  lead  was 
separated  with  vivid  incandescence,  and  made  a  hole  in  the 
crucible.  Crystals  of  silicon  also  exhibited  incandescence, 
and  set  free  metallic  lead.  Metallic  antimony  or  copper,  did 
not  liberate  lead  from  the  fused  fluoride.  By  stirring  the 
melted  fluoride  with  an  iron  rod,  the  latter  was  rapidly  cor- 
roded, heat  being  evolved,  and  lead  deposited.  Metallic 
aluminium  behaved  similarly,  but  more  rapidly.  Zinc  ex- 
ploded,  and  magnesium  detonated,  under  similar  circum- 
stances. The  latter  is  a  dangerous  experiment. 

Articles  of  zinc  or  tin,  but  not  of  iron,  become  coated 
with  lead  by  simple  immersion,  in  a  liquid  formed  by  boiling 
litharge  in  a  solution  of  caustic  potash.  Those  of  iron, 
but  not  of  copper,  coat  themselves  with  lead  by  mere  im- 
mersion, in  a  solution  of  plumbic  acetate,  />.,  sugar  of  lead. 

Deposition  of  lead  by  contact  with  a  second  metal. — (See 
also  p.  83.) — F.  Weil  coats  articles  with  lead,  by  a  similar 
process  to  that  he  employs  for  tin  (see  p.  266  ),  using  a  salt 
of  lead  instead  of  one  of  tin.  And  to  produce  a  deposit  of 
lead  free  from  zinc,  he  uses  similar  means  to  those  described 
for  tin  ('  Chemical  News,'  vol.  xiii.  p.  2).  According  to 
Becquerel,  if  a  piece  of  bright  copper  in  contact  with  zinc, 
be  immersed  in  a  solution  of  chloride  of  lead  and  sodium, 
the  copper  becomes  covered  with  lead  ('  Chemist,'  vol.  v. 
p.  408).  I  connected  together  a  wire  of  zinc,  and  one  of 
platinum,  and  immersed  them  in  a  solution  of  litharge  in 
aqueous  ammonia;  both  became  coated  with  a  black 
powder  in  a  few  minutes.  The  deposit,  moist  with  the  liquid, 
became  yellow  by  contact  with  the  air,  and  was  apparently 
re-converted  into  litharge. 

Haeffelly  coats  copper  or  brass  with  lead,  by  immersing 
it  in  contact  with  a  bar  of  tin,  in  a  hot  alkaline  solution  of 
oxide  of  lead.  The  tin  dissolves  in  the  form  of  an  alkaline 


Deposition  of  Lead  by  Separate  Current.       259 

stannate,  but  the  lead  is  precipitated  in  a  spongy  state 
('  Chemical  News,'  vol.  vi.  p.  163). 

Deposition  of  lead  by  separate  current. — (See  also  p.  89.) 
— According  to  Faraday,  fused  protoxide  of  lead  yields  metal 
at  the  cathode,  and  oxygen  at  the  anode  ;  the  chloride  gives 
lead  at  the  cathode,  and  chlorine  at  the  anode;  and  the  borate 
liberates  metal  at  the  cathode,  and  oxygen  and  boracic  acid 
at  the  anode.    Beetz  electrolysed  fused  plumbic  fluoride,  and 
observed  that  a  colourless  gas  was  evolved  from  the  positive 
pole,  and  lead  set  free  at  the  negative  pole  ('  Poggendorf's 
*  Annalen  ; '  also  *  The  Chemist,'  new  series,  vol.  i.  p.  253) 
Fremy  also  electrolysed  it  in  a  platinum  vessel,  and  found 
it  easily  decomposed,  the  lead  was  set  free,  and  alloyed  with 
the  vessel  ('Chemist,'  new  series,  vol.  ii.  p.  548).     I  also 
electrolysed  400  grains  of  pure  fluoride  of  lead  (melted  in 
a  thick  copper  crucible),  with  a  current  from  six  Smee's 
cells,  using  a  platinum  wire  as  an  anode,  and  one  of  copper 
as  the  cathode;  conduction  was  copious,  and  a  bulky  crust 
quickly  formed  upon  the  cathode,  and  advanced  towards  the 
anode  in  lumpy  projections.     A  little  gas  appeared  at  the 
latter,  but  during  a  short  time  only.     The  deposit  upon  the 
cathode  was  not  lead,  nor  was  there  any  metal  contained 
in  a  free  state  in  it,  or  in  the  saline  mass,  after  action  lasting 
one  hour ;  it  was  a  mass  of  lead-salt,  brittle,  and  of  a  red- 
brown  colour  (like  that  of  peroxide  of  lead),  when   cold 
The  conduction  was  very  perfect,  and  the  fusetl  salt  appeared 
to  conduct  without  being  decomposed.     The  anode  was  not 
corroded.      I  also   electrolysed  the   fused  salt  in  a  deep, 
narrow,  and  thick  copper  cup,  with  an  anode  of  gas-carbon, 
during  one  and  a  quarter  hours  ;  the  latter  was  corroded,  and 
the  metal  liberated;  action  was  copious,  gas  was  evolved 
at  the  anode,  and  about  seven  or  eight  cubic  inches  were 
collected.     G.  J.  Knox  also  electrolysed  fused  fluoride  of 
lead  with  an  anode  of  charcoal,  a  platinum  wire  cathode, 
and   a   current    from   sixty   voltaic    cells    ('  Philosophical 
Magazine,'  third  series,  vol.  xvi.  p.  192). 

S  2 


260  The  Art  of  Electro-Metallurgy. 

Lead  may  be  deposited  from  an  aqueous  solution,  either 
of  its  nitrate  or  acetate,  by  means  of  a  separate  current, 
with  an  anode  of  lead ;  also  from  a  liquid,  formed  by  satu- 
rating a  boiling  solution  of  caustic  potash  with  litharge ;  but 
it  is  difficult  to  obtain  any  considerable  thickness  of  reguline 
metal  from  either  of  these  liquids.  The  nitrate  and  acetate, 
yield  peroxide  of  lead  at  the  anode. 

Deposition  of  peroxide  of  lead. — Electro-chromy. — Accord- 
ing to  W.  Wernicke,  an  alkaline  solution  of  the  tartrate 
of  lead  and  sodium,  with  platinum  electrodes,  and  a  cur- 
rent from  two  Daniell's  cells,  yields  a  black  deposit  of 
peroxide  of  lead  upon  the  anode ;  and  a  solution  of  one 
part  of  plumbic  nitrate  and  eight  of  water,  gives  a  similar 
deposit  by  such  treatment  ('Journal  of  the  Chemical 
Society,'  vol.  ix.  p.  306  ;  '  Chemical  News/  vol.  xxii.  p. 
240). 

Nobili  in  the  year  1826,  discovered,  that  if  a  solution  of 
acetate  of  lead  be  electrolysed,  by  means  of  a  large  sheet 
platinum  anode,  and  a  platinum  wire  cathode,  a  deposit  is 
formed  upon  the  positive  plate  ;  and  that  if  a  polished  steel 
plate  be  employed  as  the  anode,  with  a  current  from  four  or 
six  Grove's  cells,  the  deposit  is  in  the  form  of  a  thin  film,  and 
exhibits  all  the  colours  of  the  spectrum  ;  and  by  placing  the 
positive  plate  horizontally  beneath  the  vertical  negative  wire, 
the  colours  were  in  the  form  of  rings,  the  centre  of  which  was 
the  wire,  and  were  arranged  in  the  order  of  the  chromatic 
scale.  These  colours  are  known  as  '  Nobili's  rings.'  Becque- 
rel,  Gassiot,  and  others,  have,  by  varying  the  strength  of  the 
battery,  and  of  the  solutions  employed,  and  interposing  non- 
conducting patterns  between  the  anode  and  cathode,  and  by 
using  cathodes  of  different  shapes,  obtained  effects  of  great 
delicacy  and  beauty.  Salts  of  other  metals,  such  as  man- 
ganese, bismuth,  cobalt,  nickel,  &c.,  which  yield  deposits  of 
peroxide  of  the  anodes  (see  pp.  112,  235,  242,  252),  may  be 
employed  instead  of  those  of  lead.  Becquerel  obtained  films 
of  peroxide  of  iron,  by  electrolysing  in  vacuo,  a  solution  of 


Electro-  Chromy.  26 1 

protoxide  of  iron  in  liquid  ammonia  ('  Chemist,'  vol.   iv. 

P-  457). 

The  colours  occur,  sometimes  upon  the  anodes,  and 
sometimes  upon  the  cathodes,  according  to  the  liquid 
employed,  and  with  a  variety  of  metals  in  a  number  of  dif- 
ferent liquids.  At  other  times,  they  arise  wholly  from  deposits 
from  the  liquid,  as  with  peroxides  on  anodes  of  platinum, 
or  films  of  metal  upon  the  cathodes ;  and  sometimes  they  con- 
sist of  insoluble  substances,  formed  by  the  union  of  the  anode 
with  an  element  of  the  liquid. 

Becquerel  prepared  his  plumbic  solution  as  follows  : — 
Dissolve  200  grammes  of  caustic  potash  in  two  quarts  of 
distilled  water,  add  150  grammes  of  litharge,  boil  the 
mixture  half  an  hour,  allow  it  to  become  clear,  take  the  clear 
portion,  and  dilute  it  with  its  own  bulk  of  water  ('  The 
Chemist/  vol,  iv.  p.  457).  The  solution  is  used  cold,  and 
is  rapidly  deprived  of  its  metal,  because  'ead  is  deposited 
upon  the  cathode  at  the  same  time. 

By  this  means  may  be  imparted  to  polished  surfaces  of 
metals,  all  the  richest  colours  of  the  rainbow.  'They 
commence  with  silver  blonde,  and  progress  onwards  to  fawn 
colour,  and  thence  through  various  shades  of  violet  to  the 
indigo  and  blues  ;  then  through  pale  blue  to  yellow  and 
orange  ;  thence  through  lake  and  bluish  lake  to  green  and 
greenish  orange,  and  rose  orange  ;  thence  through  greenish 
violet  and  green,  to  reddish  yellow  and  rose  lake,  which  is 
the  highest  colour  on  the  chromatic  scale '  (Walker's  '  Electro- 
type Manipulation/  part  ii.  i6th  edition,  p.  40).  Too  great  a 
strength  of  the  current  covers  all  the  tints  with  a  uniformly 
dark  brown  coating.  The  deposits,  if  properly  prepared, 
resist  friction  well. 

Metallo-chromy,  effected  by  means  of  a  solution  of  oxide 
of  lead  in  caustic  soda  or  potash,  is  largely  employed  in 
Nuremberg,  to  ornament  metallic  toys  (Wagner's  'Tech- 
nology/ p.  117).  Bells  are  similarly  coloured  in  France, 
and  the  hands  and  dials  of  watches  in  Switzerland. 


262  The  A  rt  of  Electro- Metallurgy. 

26.  Thallium.— Elec.  -chem.  eqt.  =  204.  Solutions  of 
this  metal  are  easily  formed,  by  making  a  piece  of  it 
the  anode,  for  a  sufficient  length  of  time,  in  the  respective 
acids,  sufficiently  diluted  to  dissolve  the  compounds.  The 
sulphate  is  one  of  the  most  soluble  salts,  and  requires  about 
twenty  times  its  weight  of  water  to  dissolve  it. 

According  to  A.  Cossa,  aluminium  deposits  metallic  thal- 
lium from  a  hot  solution  of  its  chloride  (*  Watts's  Dictionary 
of  Chemistry,'  vol.  vii.  p.  54).  Zinc  coats  itself  with  metal  in 
solutions  of  salts  of  thallium,  but  tin  does  not.  Accord- 
ing to  Lamy,  zinc  precipitates  it  from  the  solution  of 
the  sulphate  and  nitrate,  in  the  form  of  brilliant  crystalline 
laminae.  I  found  that  crystals  of  silicon  had  no  reducing 
effect,  upon  a  solution  of  fluoride  of  thallium,  containing  free 
hydrofluoric  acid. 

Electrolysis  of  salts  of  thallium. — Solutions  of  the  salts  of 
thallium  are  easily  decomposed  by  a  feeble  electric  current; 
and  the  metal  deposited  in  the  form  of  beautiful  crystalline 
plates  upon  the  cathode.  When  one  of  the  sulphate  is 
electrolysed  by  a  weak  current,  brown  thallic  peroxide  is 
deposited  upon  the  anode. 

I  electrolysed  an  aqueous  solution  of  the  fluoride,  by 
means  of  one  Smee's  cell,  a  thallium  anode,  and  a  platinum 
cathode.  It  conducted  freely,  and  quickly  yielded  a  deposit 
of  the  metal,  in  long  feathery  crystals,  like  those  of  electro- 
deposited  tin,  but  of  a  less  white  colour. 

Thallium  deposits  metal  from  the  sulphate,  nitrate,  and 
acetate  of  copper,  nitrate  of  silver,  solutions  of  gold,  mer- 
curous  sulphate,  and  acetate  of  lead,  but  a  basic  salt  from 
nitrate  of  cobalt  (W.  C.  Reid,  '  Chemical  News,'  vol.  xii. 
p.  242). 

27.    Indium.— Elec.-chem.  eqt.  =-1114  =  3 7-8.     This 

metal  being  at  present  very  costly,  little  has  been  done  with 
it  in  electro- metallurgy.  It  is  allied  to  thallium  and  aluminium. 
Its  salts  are  generally  freely  soluble  in  water ;  the  double 


Salts  of  Tin.  263 

sulphate  of  indium  and  potassium,  called  indium-alum,  dis- 
solves in  half  its  weight  of  water  at  16°  C. 

Indium  is  precipitated  as  metal  from  the  solutions  of  its 
salts,  by  means  of  zinc.  A  solution  of  the  sulphate  or  chlo- 
ride, may  be  used  for  this  purpose. 

28.  Tin,  Elec.  chem.  eqt.  =  —  =  29-5.      The  com- 

4 

monest  salts  of  tin,  are  stannous  and  stannic  oxides,  the 
two  chlorides,  the  sulphides  of  tin,  and  the  stannates  of 
sodium  and  potassium.  Stannous  chloride  is  the  most  use- 
ful salt,  and  should  be  freshly  prepared,  because  it  becomes 
less  soluble  by  being  kept  a  long  time  exposed  to  the  air ;  it 
may  be  easily  made,  by  adding  abundance  of  fragments  of 
pure  tin  to  strong  hydrochloric  acid,  and  keeping  the  acid  hot, 
until  it  has  acquired  an  oily  consistence,  and  gas  ceases  to 
be  evolved.  Stannic  oxide  may  be  prepared,  by  pouring  the 
anhydrous  bichloride  very  gradually  into  water,  with  stirring, 
and  then  adding  sufficient  ammonia  to  precipitate  the  oxide. 
Wash  the  precipitate. 

A  protochloride  of  tin  depositing  liquid,  may  be  easily 
formed,  by  dissolving  the  ordinary  commercial  salt  in  water, 
and  adding  a  little  hydrochloric  acid,  to  remove  any  cloudi- 
ness which  may  appear  ;  a  similar,  but  better  liquid,  may  be 
made  by  the  battery  process,  by  passing  the  current  through 
dilute  hydrochloric  acid,  by  means  of  a  large  tin  anode,  until 
sufficient  metal  is  dissolved.  This  (or  the  other  chloride  of 
tin)  is  not  a  good  solution  to  obtain  reguline  metal  from ; 
it  has  a  very  great  tendency  to  deposit  the  tin  in  the  form 
of  long  crystalline  needles,  of  a  fernlike  appearance,  which 
often  project  from  the  corners  and  edges  of  the  cathode,  to 
a  distance  of  upwards  of  half  an  inch.  A  solution  composed 
of  eleven  ounces  of  water,  one  of  hydrochloric  acid,  and 
eighty  grains  of  protochloride  of  tin,  admits  of  this  effect 
being  produced  in  a  striking  manner.  Nearly  all  the  com- 
pounds of  tin,  and  especially  those  formed  with  mineral 
acids,  exhibit  this  tendency  in  a  greater  or  less  degree,  when 


264  The  Art  of  Electro-Metallurgy. 

acted  upon  by  electrolysis,  rendering  the  deposition  of  tin  in 
thick  layers  of  fine  white  coherent  metal,  a  matter  of  con- 
siderable difficulty. 

The  stannate  of  potash  solution  is  made,  either  by  dis- 
solving the  solid  salt  in  water,  or  mixing  freshly  precipitated 
peroxide  of  tin  (whilst  still  moist)  with  a  boiling  solution 
of  caustic  potash.  It  may  also  be  easily  formed  by  the  battery 
process,  by  passing  a  strong  current  of  electricity,  by  means 
of  a  large  tin  anode,  through  a  strong  and  boiling  solution  of 
caustic  potash,  until  the  immersed  cathode  receives  a  free 
white  deposit.  This  solution,  if  used  at  150°  Fahr.,  yields 
fine  white  tin ;  but  it  decomposes  by  exposure  to  the 
atmosphere,  and  soon  deposits  its  metal  as  oxide,  at  the 
bottom  of  the  vessel.  A  solution  of  cyanide  of  potassium 
and  of  tin,  has  been  proposed  as  a  depositing  liquid  ;  but 
it  is  a  bad  conductor  with  a  tin  anode,  even  if  hot,  and  does 
not  dissolve  the  metal  freely. 

Electrical  relations  of  tin  and  iron. — Tin  is  feebly 
negative  to  iron  at  all  temperatures  between  62°  and  203° 
Fahr.  in  distilled  water,  and  positive  to  it  at  212°  Fahr.  It 
is  positive  to  iron  at  all  temperatures  between  62°  and  212° 
Fahr.  in  a  saturated  solution  of  boracic  acid  ;  also  the  same 
between  those  temperatures,  in  a  strong  solution  of  phos- 
phoric acid  in  distilled  water,  or  in  one  measure  of  oil  of 
vitriol,  mixed  with  either  nine  or  ninety-six  of  distilled 
water  ;  or  in  a  mixture  of  one  measure  of  this  acid,  and  192 
of  distilled  water,  from  73°  to  158°  Fahr.,  and  negative  to 
iron  above  that  to  212°  Fahr.;  it  is  positive  to  iron  from  72° 
to  212°  Fahr.  in  a  mixture  of  equal  measures  of  hydro- 
chloric acid  and  water;  it  is  negative  to  iron  from  70°  to 
77°  Fahr.,  and  positive  above  that  to  212°  Fahr.,  in  a  mixture 
of  one  measure  of  hydrochloric  acid,  and  nine  of  distilled 
water;  it  is  negative  to  iron  from  70°  to  212°  Fahr.  in  a 
mixture  of  one  measure  of  hydrochloric  acid,  and  ninety 
of  distilled  water,  and  positive  to  iron  from  68°  to  212° 
Fahr.,  in  one  measure  of  hydrofluoric  acid,  and  nine  of 


Deposition  of  Tin  by  Simple  Immersion.      26$ 

water;  it  is  positive  to  iron  in  one  measure  of  nitric  acid, 
and  nine  of  water  from  70°  to  1 1 1°  Fahr.,  and  negative 
from  iu°  to  212°  Fahr.  ;  and  it  is  positive  to  iron  from  82° 
to  212°  Fahr.  in  a  mixture  of  one  measure  of  nitric  acid, 
and  ninety-six  of  water. 

Deposition  of  tin  by  simple  immersion.—  (See  also  p.  79.) 
— I  found  that  crystals  of  silicon,  did  not  deposit  tin  from  a 
solution  of  stannous  fluoride  containing  free  hydrofluoric 
acid;  and  that  zinc  immersed  in  a  solution  of  stannic 
fluoride,  evolved  gas,  and  produced  a  flocculent  precipitate. 

A  remarkable  instance  of  deposition  of  tin,  is  mentioned 
by  M.  Henri  Loewel.  He  added  metallic  tin  to  a  solu- 
tion of  green  crystallised  chloride  of  chromium  (which  did 
not  contain  an  excess  of  acid),  in  a  closed  glass  vessel, 
and  boiled  the  mixture  ten  or  twelve  minutes,  and  allowed 
it  to  cool.  During  the  heating,  the  tin  dissolved,  and  took 
chlorine  from  some  of  the  chromium  salt,  forming  proto- 
chloride  of  tin  and  protochloride  of  chromium.  But  during 
the  cooling,  a  reverse  action  occurred,  the  protochloride  oif 
chromium  removed  the  chlorine  from  the  other  protochloride, 
and  the  tin  was  deposited  in  the  form  of  numerous  small 
metallic  plates  ('  The  Chemist,'  part  viii.  May,  1854,  p.  476). 

Magnesium  deposits  stannic  acid,  and  spongy  tin,  from 
a  solution  of  stannous  chloride  (Commaille,  'Chemical 
News,'  vol.  xiv.  p.  188).  A  tin  tree,  is  produced  by  immer 
sing  a  rod  of  zinc,  or  a  spiral  of  zinc  wire,  in  ten  or  twenty 
ounces  of  water  to  which  have  been  added  three  drachms  of 
stannous  chloride,  and  ten  drops  of  nitric  acid,  and  allowing 
the  liquid  and  zinc  to  remain  undisturbed. 

To  coat  brass  pins,  and  other  small  articles  of  copper  or 
brass,  with  tin,  they  are  placed  in  layers  between  sheets  of 
grain  tin,  in  a  saturated  solution  of  cream  of  tartar,  and  the 
liquid  boiled.  A  little  stannous  chloride  may  also  be  added 
if  necessary. 

Clean  articles  of  copper,  bronze,  or  brass,  in  contact 
with  cuttings  of  tin,  in  a  boiling  solution  of  peroxide  of  tin 


266  The  A  rt  of  Electro-Metallurgy. 

in  caustic  potash,  become  coated  in  a  few  minutes  with  a 
beautiful  layer  of  metal.  The  solution  may  also  be  used  for 
tinning  iron,  by  the  battery  process,  with  large  anodes  of  tin, 
and  may  be  made  to  give  a  very  fine  deposit,  but  it  precipi- 
tates its  metal  gradually,  in  the  form  of  a  white  powder,  by 
contact  with  the  air  (see  p.  264). 

C.  Paul  tins  articles  of  zinc,  iron,  brass,  copper,  &c.,  in  the 
following  manner  : — The  zinc  or  iron  articles,  are  immersed 
in  a  mixture  of  ten  parts  of  water,  and  one  of  sulphuric 
or  nitric  acid,  and  a  dilute  solution  of  cupric  sulphate  is 
then  slowly  added,  with  stirring.  After  a  thin  layer  of  cop- 
per is  deposited,  the  articles  are  removed,  washed,  wetted 
with  a  solution,  composed  of  one  part  of  crystals  of 'stannous 
chloride,  two  of  water,  and  two  of  hydrochloric  acid,  and 
then  shaken  with  a  mixture  of  finely  powdered  chalk,  and 
sulphate  of  copper  and  ammonium,  which  is  prepared  by 
dissolving  one  part  of  cupric  sulphate  in  sixteen  of  water, 
and  adding  aqueous  ammonia,  until  a  clear  dark  blue  liquid 
is  formed.  The  articles  are  now  tinned  by  immersion  in  a 
solution,  composed  of  one  part  of  crystals  of  stannous  chlo- 
ride, and  three  of  white  argol,  dissolved  in  water  ('  Journal 
of  the  Chemical  Society/  vol.  xi.  p.  955). 

To  coat  articles  of  iron  or  zinc  with  tin,  dissolve  one 
part  of  fused  stannous  chloride,  and  thirty  of  ammonium- 
alum,  in  2,000  of  water,  heat  the  solution  to  boiling,  and 
immerse  the  previously  cleaned  articles  in  it  until  they 
attain  a  fine  white  colour;  add  to  the  solution  as  it  becomes 
weaker,  small  quantities  of  the  stannous  chloride.  Accord- 
ing to  Roseleur,  articles  of  zinc  may  also  be  tinned  by  sim- 
ple immersion,  in  a  solution  composed  of  one  part  of  fused 
stannous  chloride,  and  five  of  pyrophosphate  of  sodium, 
dissolved  in  300  of  distilled  water.  Tin  which  has  been 
dissolved  from  the  surface  of  tinned  iron,  is  sometimes 
reduced  to  metal,  by  immersion  of  pieces  of  zinc  in  the 
solution. 

According  to  Becquerel,  copper,  and  iron,  do  not  coat 


Electro-Deposition  of  Tin.  267 

themselves  with  tin,  in  a  dilute  solution  of  the  double  chlo- 
ride of  tin  and  sodium,  at  160  Fahr.,  but  are  readily  tinned 
in  that  liquid  by  contact  with  zinc  (*  The  Chemist,'  vol.  v. 
p.  408). 

Depositing  tin  by  contact  with  a  second  metal. — (See  also 
p.  83.) — For  coating  articles  of  iron  with  tin,  by  means  of 
contact  with  zinc,  Roseleur  recommends  the  two  following 
liquids: — No.  i.  Take  equal  weights  of  distilled  water,  stan- ' 
nous  chloride,  and  cream  of  tartar,  dissolve  the  tin  salt  in 
one-third  of  the  cold  water,  warm  the  remainder  of  the  water, 
dissolve  the  cream  of  tartar  in  it,  and  mix  the  solutions ; 
the  liquid  is  clear,  and  has  an  acid  reaction.  No.  2.  Dis- 
solve six  parts  of  crystals,  or  four  of  fused  stannous  chlo- 
ride, and  sixty  of  pyrophosphate  of  potassium  or  sodium, 
in  3,000  of  distilled  water,  and  stir  the  mixture;  the  liquid 
is  clear.  Each  solution  is  used  hot,  and  kept  in  constant 
motion.  The  articles  are  immersed  in  contact  with  fragments 
of  zinc,  the  total  amount  of  surface  of  which  is  about  ^0-th 
that  of  the  articles.  The  process  of  deposition  occupies  from 
one  to  three  hours.  Equal  weights  of  pyrophosphate,  and  of 
fused  stannous  chloride,  are  added  occasionally. 

According  to  F.  Weil,  copper,  and  coppered  metals,  as 
well  as  iron  and  steel,  may  be  tinned,  by  dissolving  a  salt  of 
tin  in  a  strong  solution  of  potash  or  soda,  and  immersing  the 
articles  in  the  liquid  in  contact  with  zinc  ;  the  solution  being 
at  from  50°  to  100°  C. :  the  deposit,  however,  contains  zinc,- 
To  obtain  a  pure  deposit,  of  increasing  thickness,  place  in 
the  vessel  containing  the  tin  solution,  a  porous  cell  contain- 
ing the  alkaline  liquid  (without  tin-salt)  and  the  zinc.  Put 
the  article  to  be  tinned,  in  the  outer  liquid,  and  connect  it 
with  the  zinc  by  a  wire.  To  revive  the  inner  liquid,  precipi- 
tate the  dissolved  zinc,  by  addition  of  sulphide  of  sodium 
('Chemical  News/  vol.  xiii.  p.  2). 

Dr.  Hillier  uses  for  tinning  metals,  a  solution  composed 
of  one  part  of  stannous  chloride  and  twenty  of  water, 
to  which  is  next  added  a  solution  of  two  parts  of  caustic 


268  The  A  rt  of  Electro-Metallurgy. 

soda,  in  twenty  of  water;  the  mixture  is  heated.  The  articles 
are  placed  upon  a  perforated  plate  of  block  tin  in  the  hot 
liquid,  and  agitated  with  a  rod  of  zinc  until  they  are  suffi- 
ciently coated  ('  Chemical  News,'  vol.  xx.  p.  84). 

Tinning  iron  wire :  by  M.  Heeren. — The  wire  is  first 
cleaned  in  a  hydrochloric  acid  bath  in  which  a  piece  of  zinc  is 
suspended.  The  cleaned  wire  is  then  brought  into  contact 
with  a  plate  of  zinc,  in  a  bath  in  which  two  parts  of  tartaric 
acid  are  dissolved  in  100  of  water,  with  further  addition  of 
three  parts  of  stannous  chloride,  and  three  of  soda  ;  and 
after  remaining  about  two  hours  in  the  liquid,  the  wire  is 
brightened  by  drawing  it  through  a  hole  in  a  steel  plate 
('Journal  of  the  Chemical  Societ}7/  vol.  xiii.  p.  672). 

F.  Stolba  uses,  for  tinning,  a  carefully  made  solution  of 
.protochloride  of  tin,  containing  from  5  to  10  per  cent  of  that 
salt,  to  which  mixture  a  small  pinch  of  cream  of  tartar 
has  been  added.  The  article,  previously  well  cleaned,  is 
rubbed  over  with  the  solution,  and  then  with  powdered  zinc  ; 
it  is  then  washed,  and  polished  with  soft  whiting  ('  Chemical 
News/  vol.  xxiii.  p.  21). 

According  to  Raoult,  gold  or  copper  in  contact  with  tin, 
in  a  concentrated  and  boiling  solution  of  stannous  chloride, 
receives  a  deposit  of  tin.  But  gold  in  contact  with  iron, 
nickel,  antimony,  lead,  copper,  or  silver,  receives  no  such 
coating,  either  in  the  hot  or  cold  solutions  ('  Chemical  News,' 
vol.  xxvi.  p.  240  ;  vol.  xxvii.  p.  59;  'Journal  of  the  Chemical 
Society,'  vol.  xi.  p.  464). 

Electrolysis  of  salts  of  tin. — Fused  stannous  cKloride, 
yields  tin  at  the  cathode,  and  stannic  chloride  escapes  in 
vapour  at  the  anode  (Faraday).  Fremy  electrolysed  fused 
fluoride  of  tin  in  a  platinum  vessel;  it  was  easily  decomposed  ; 
but  the  deposited  metal  alloyed  with,  and  perforated,  the 
vessel  in  a  few  minutes  ('  The  Chemist/  new  series,  vol.  ii. 
p.  548).  Anhydrous  tetrachloride  of  tin  did  not  conduct  a 
current  from  8,040  cells  of  W.  de  la  Rue's  chloride  of  silver 
battery  ('  Proceedings  of  the  Royal  Society,'  vol.  xxv.  p.  325). 


Deposition  of  Crystals  of  Tin,  269 

I  electrolysed  a  saturated  non-acid  solution  of  stamious 
fluoride,  by  means  of  large  platinum  electrodes,  and  a  current 
from  ten  large  Smee's  elements ;  the  conduction  was  sparing ; 
a  little  oxygen  was  evolved  from  the  anode,  and  long  feathery 
crystals  of  tin  were  slowly  formed  upon  the  cathode.  No 
gas  was  evolved  from  the  cathode,  nor  deposit  formed  upon 
the  anode.  In  another  experiment,  with  one  Smee's  cell,  and 
a  copper  cathode,  the  deposit  of  tin  was  white,  and  beautiful 
crystals  of  the  metal  soon  reached  across  the  liquid  and 
touched  the  anode. 

By  passing  a  current  from  six  Grove's  elements,  by  means 
of  platinum  electrodes,  through  a  strong  solution  of  stannic 
fluoride,  containing  little  or  no  free  hydrofluoric  acid,  a  grey 
deposit  of  metallic  tin  soon  occurred.  There  was  free  con- 
duction, much  gas  from  the  anode,  and  heat  evolved  in  the 
liquid.  The  anode  was  not  corroded  nor  received  any  solid 
deposit. 

To  obtain  crystals  of  tin  by  electrolysis. — The  crystallisa- 
tion of  tin,  is  a  phenomenon  conspicuously  striking,  under 
some  conditions,  in  a  solution  of  stannous  chloride.  The 
crystals  of  tin  formed  upon  the  cathode,  increase  so  rapidly 
in  length,  as  to.  grow  across  the  solution,  and  touch  the  posi- 
tive pole  in  a  few  minutes.  And  if  the  solution  and  current 
are  strong,  and  the  cathode  small,  quite  a  mass  of  crystals 
will  soon  fill  the  liquid,  and  converge  towards  the  anode. 
If  the  anode  be  dr^wn  farther  away  in  the  solution,  the 
crystals  follow  it.  The  largest  crystals  are  produced  by 
slow  action :  to  produce  them,  a  platinum  capsule  is  covered 
with  an  outer  coating  of  wax,  leaving  the  bottom  uncovered, 
and  then  set  upon  a  plate  of  amalgamated  zinc  in  a  porcelain 
vessel.  The  capsule  is  then  filled  completely  with  a  dilute 
and  not  too  acid  solution  of  stannous  chloride,  whilst  the 
outer  vessel  is  filled  with  water  (containing  one-twentieth  its 
bulk  of  hydrochloric  acid),  up  to  such  a  height,  that  the  two 
liquids  come  into  mutual  contact.  The  electric  current 
generated,  reduces  the  salt  of  tin,  and  in  a  few  days  the  crys- 


2  70  The  A  rt  of  Electro-Metallurgy. 

tals  upon  the  interior  of  the  capsule  are  well  developed,  and 
should  be  washed  with  water  and  dried  quickly  (F.  Stolba, 
*  Chemical  News,'  vol.  xxx.  p.  177). 

Deposition  of  tin  by  separate  current  process. — (See  also 
p.  89.) — There  are  many  solutions  for  electro-tinning  by 
means  of  a  separate  current,  but  only  a  very  few  have  been 
extensively  used.  Most  of  them  alter  in  property  by  contact 
with  the  atmosphere,  and  deposit  their  metal  as  a  white 
oxide.  Roseleur  uses  a  solution,  composed  of  five  parts  of 
fused  (or  six  of  crystals)  stannous  chloride,  and  fifty  of  pyro- 
phosphate  of  potassium  or  sodium,  added  to  5,000  of 
distilled  water ;  the  chloride  is  dissolved  in  a  portion  of  the 
water,  and  added  the  last,  and  the  liquid  is  stirred  until  it  is 
clear.  A  very  large  surface  of  anode  is  employed,  and  a 
strong  electric  current.  As  less  tin  is  dissolved  than  is  depo- 
sited, it  is  necessary  to  add  occasionally,  equal  weights  of  the 
pyrophosphate  and  fused  chloride. 

Fearn's  patent  process  for  tinning,  has  been  worked  in 
Birmingham.  The  liquids  employed  are  prepared  as  fol- 
lows : — 

No.  i.  A  solution  of  stannous  chloride  (not  containing 
much  free  acid)  is  first  made,  containing  three  ounces  of 
metallic  tin  per  gallon.  Thirty  pounds  of  caustic  potash 
are  also  dissolved  in  twenty  gallons  of  water,  and  thirty 
ot  pyrophospnate  of  sodium  in  sixty  gallons  of  water.  Two 
hundred  ounces  by  measure  of  the  tin  solution,  are  poured 
slowly  (whilst  stirring  with  a  glass  rod)  into  the  twenty 
gallons  of  potash  liquid  ;  the  precipitate  formed  re-dissolves 
quickly;  into  this  liquid  is  poured,  first  all  the  cyanide 
solution,  and  then  all  the  pyrophosphate,  and  the  mixture 
stirred. 

No.  2.  Fifty-six  pounds  of  salammoniac  are  dissolved 
in  sixty  gallons  of  water,  and  twenty  of  pyrophosphate  of 
sodium  in  forty  gallons  of  water  ;  and  into  the  latter  is  poured 
100  ounces  by  volume  of  the  chloride  of  tin  solution,  and 
the  mixture  stirred  j  the  precipitate  soon  re-dissolves.  The 


Electro-Deposition  of  Tin.  271 

salammoniac  solution  is  then  added  to  the  mixture,  and  the 
whole  stirred. 

No.  3.  One  hundred  and  fifty  pounds  of  salammoniac 
are  dissolved  in  100  gallons  of  water ;  and  200  fluid  ounces 
of  the  tin  solution  poured  into  it,  and  the  mixture  well  stirred. 

No.  4.  Four  hundred  ounces  of  tartrate  of  potassium,  are 
dissolved  in  fifty  gallons  of  water,  and  1,200  ounces  of  solid 
caustic  potash  in  another  fifty  gallons  ;  600  fluid  ounces  of 
the  tin  solution  are  then  added  slowly,  with  stirring,  to  the 
liquid  tartrate  ;  and  then  the  caustic  potash  solution  poured 
into  the  mixture,  with  continual  and  thorough  agitation,  to 
re-dissolve  all  the  precipitate. 

The  first  solution  is  used  at  70°  Fahr.  with  a  current  from 
two  Bunsen's  cells.  The  second  is  worked  at  100°  to  110° 
Fahr.  with  a  weaker  current.  The  third  is  used  at  70°  Fahr. 
And  the  fourth  solution  may  be  used  cold.  The  first  and 
fourth  solutions,  yield  thick  deposits,  without  requiring  alter- 
nate deposition  and  scratchbrushing.  As  during  working, 
more  tin  is  deposited  than  dissolved,  the  oxide  or  other  com- 
pound of  the  metal,  must  be  added  occasionally,  except  in 
the  case  of  the  third  solution,  which  acts  upon  the  anode  more 
freely  than  the  others.  Articles  of  cast  iron  require  to  be 
covered  with  a  thin  film  of  copper,  previous  to  being  tinned 
in  these  liquids.  Articles  of  zinc  are  tinned  in  No.  i  solu- 
tion. Further  particulars  respecting  the  means  necessary  for 
keeping  each  particular  mixture  in  proper  working  order,  are 
given  in  the  specification  of  the  patent.  The  process  is 
worked  by  the  '  Electro-stannous  Company/  in  Birmingham. 

Mr.  Joseph  Steele,  coats  zinc,  iron,  steel,  copper,  and 
brass,  with  tin,  in  his  patent  solution,  by  the  battery  process, 
thus  : — Dissolve  sixty  pounds  of  common  soda,  fifteen 
of  pearlash,  five  of  caustic  potash,  and  two  ounces  of  cyanide 
of  potassium,  in  seventy-five  gallons  of  water,  and  filter  the  re- 
sulting solution ;  then  add  two  ounces  of  acetate  of  zinc,  and 
sixteen  pounds  of  peroxide  of  tin  ;  stir  the  resulting  mixture 
until  all  is  dissolved  ;  it  is  then  ready  for  use.  Work  it 


272  The  Art  of  Electro-Metallurgy. 

by  means  of  a  separate  current,  with  an  anode  of  tin,  keeping 
the  liquid  at  75°  Fahr. 

De  Lobstein's  patent  solution,  for  tinning  by  means  of 
the  battery,  is  composed  of  500  gallons  of  water,  eighty 
pounds  of  caustic  soda,  thirty-four  ounces  of  cyanide  of 
potassium,  and  twenty- two  of  salts  of  tin,  i.e.,  stannous 
chloride. 

The  acetate  and  oxalate  of  tin,  also  oxide  of  tin  dissolved 
in  a  solution  of  cyanide  of  potassium,  have  been  tried  for 
tinning,  but  do  not  appear  to  yield  satisfactory  results. 

Processes  of  electro-tinning  are  not  extensively  used,  be- 
cause there  appears  to  be  no  great  demand  for  electro-tinned 
articles. 

Electro-deposition  of  alloys  of  copper  and  tin. — A  colour 
similar  to  that  of  bronze,  is  imparted  to  articles  of  iron  or  steel, 
by  agitating  them  for  a  long  time,  in  a  solution  composed  of 
four  to  five  parts  of  sulphate  of  copper,  and  four  to  five  of 
crystallised  stannous  chloride,  dissolved  in  100  of  water. 

F.  Weil  coats  articles  of  iron,  steel,  and  other  metals, 
with  true  bronze  (i.e.,  an  alloy  of  copper  and  tin),  by  adding 
to  his  tartrate  of  copper  bath  (see  p.  204),  some  stannate  of 
sodium,  or  a  solution  of  chloride  of  tin  previously  treated  with 
a  sufficiency  of  soda ;  and  immersing  the  articles  in  the 
mixture  in  contact  with  zinc  (see  '  Chemical  News/  vol.  xiii. 
p.  2).  Salzede  patented  (Sept.  30,  1847)  a  liquid  for  depo- 
siting bronze  by  the  batteiy  process  ;  it  consists  of  carbonate 
of  potassium,  chloride  of  copper,  chloride  of  tin,  nitrate  of 
ammonium,  and  cyanide  of  potassium,  dissolved  in  water,  and 
used  at  a  temperature  of  77°  Fahr.  A  solution  patented  by 
Newton  (July  29,  1850),  for  a  similar  purpose,  consists  of  the 
tartrates  of  copper,  tin,  and  potassium. 

M.  Weis-Kopp  imparts  a  bronze  appearance  to  electro- 
coppered  articles  of  cast  iron,  by  rubbing  them  with  a  mix- 
ture of  four  parts  of  salammoniac,  one  of  oxalic,  and  one 
of  acetic  acid,  dissolved  in  thirty  of  water  ('  Chemical  News,' 
vol.  xxi.  p.  47). 


Deposition  of  Cadmium.  273 

29.  Cadmium.— Elec.-  chem.  eqt.  =  H1  =  56-0,      The 

most  usual  salts  of  cadmium,  are  the  oxide,  nitrate,  chloride, 
bromide,  iodide,  sulphide,  and  sulphate.  The  nitrate,  chlo- 
ride, iodide,  bromide,  and  sulphate,  are  colourless,  and 
may  be  easily  prepared,  by  saturating  the  respective  acids, 
with  either  cadmium  or  its  oxide,  and  evaporating  the  solu- 
tions until  they  crystallise.  Fluoride  of  cadmium  may  be 
made,  by  adding  the  carbonate  to  an  excess  of  dilute 
hydrofluoric  acid,  and  evaporating  the  mixture  to  dryness. 
I  have  found  that  crystals  of  silicon,  heated  with  this  salt, 
separate  the  metal. 

From  a  solution  of  the  chloride,  magnesium  deposits, 
with  strong  action,  a  mixture  of  cadmium  and  an  oxy- 
chloride  of  that  metal.  (Commaille,  '  Chemical  News/ 
vol.  xiv.  p.  1 88.) 

Deposition  of  cadmium  by  contact  with  another  metal. — 
According  to  Raoult,  gold,  or  copper,  in  contact  with  cad- 
mium, in  a  concentrated  and  boiling  solution,  of  cadmium 
sulphate,  or  chloride,  decomposes  these  salts,  and  quickly 
deposits  a  white,  brilliant,  and  firmly  adherent,  but  thin  film 
of  cadmium,  upon  the  gold  or  copper,  even  when  the  solution 
is  not  acidulated  and  no  hydrogen  is  evolved.  The  experi- 
ment does  not  succeed  with  the  nitrate.  But  gold,  in 
contact  with  iron,  nickel,  antimony,  lead,  copper,  or  silver, 
in  cold  or  boiling,  acid  or  neutral,  solutions  of  salts  of 
cadmium,  receives  no  such  deposit  ('Chemical  News,' 
vol.  xxvi.  p.  240;  vol.  xxvii.  p.  59;  'Journal  of  the 
Chemical  Society,'  vol.  xi.  p.  464). 

Deposition  of  cadmium  by  means  of  a  separate  current. — 
According  to  Smee,  it  is  difficult  to  obtain  firm,  coherent, 
deposits  of  this  metal,  from  solutions  of  either  its  chloride 
or  sulphate,  but  it  may  be  easily  deposited  in  a  reguline 
flexible  state,  from  a  solution  of  the  ammonio-sulphate,  pre- 
pared by  adding  sufficient  aqueous  ammonia,  to  a  solution  of 
sulphate  of  cadmium,  to  re-dissolve  the  precipitate. 

T 


2/4  The  Art  of  Electro-Metallurgy. 

A  patent  was  taken  out  (March  19,  1849),  by  Messrs. 
Russell  and  Woolrich,  for  the  electro-deposition  of  this  metal, 
arid  the  following  is  their  description  of  the  process  : — 
'  Take  cadmium,  and  dissolve  it  in  nitric  acid  diluted  with 
five  or  six  times  its  bulk  of  water,  at  a  temperature  of  about 
80°  or  100°  Fahr.,  adding  the  dilute  acid  by  degrees  until 
the  metal  is  all  dissolved ;  to  this  solution  of  cadmium, 
one  of  carbonate  of  sodium  (made  by  dissolving  one 
pound  of  the  ordinary  crystals  of  washing  soda  in  one  gallon 
of  water)  is  added  until  the  cadmium  is  all  precipitated ; 
the  precipitate  thus  obtained,  is  washed  four  or  five  times 
with  tepid  water ;  next  add  as  much  of  a  solution  of  cyanide 
of  potassium  as  will  dissolve  the  precipitate  ;  after  which 
one-tenth  more  of  the  solution  of  potassium  salt  is  added 
to  form  free  cyanide.  The  strength  of  this  mixture  may 
vary,  but  the  patentees  prefer  a  solution  containing  six  troy 
ounces  of  metal  to  the  gallon.  The  liquid  is  worked  at 
about  1 00°  Fahr.  with  a  plate  of  cadmium  as  an  anode.' 
Very  little  has  yet  been  done  in  the  practical  electro-depo- 
sition of  this  metal. 

M.  A.  Bertrand  recommends,  for  depositing  cadmium,  a 
solution  of  its  bromide,  containing  a  little  sulphuric  acid  ; 
also  one  of  its  sulphate ;  and  says  the  deposit  obtained  is 
white,  adheres  firmly,  is  very  coherent,  and  is  capable  of 
receiving  a  fine  polish  ('  Chemical  News/  vol.  xxxiv.  p. 
227). 

30.    Zinc,  —  Elec.  chem.  eqt.  =  -5  =  32-5.     The  most 

common  salts  of  zinc  are  the  oxide,  chloride,  carbonate,  and 
sulphate.  The  oxide  may  be  formed,  by  precipitating  a 
solution  of  the  sulphate  with  aqueous  ammonia,  and  washing 
the  precipitate  ;  the  carbonate,  by  precipitating  such  a  solu- 
tion by  means  of  washing  soda.  The  various  soluble  salts, 
such  as  the  nitrate,  chloride,  bromide,  sulphate,  acetate,  &c., 
may  be  easily  formed,  by  digesting,  until  it  ceases  to  dissolve, 
an  excess  of  metallic  zinc,  its  oxide,  or  carbonate,  with  the 


Deposition  of  Zinc  by  Simple  Immersion.       275 

corresponding  acid,  diluted  with  water,  and  evaporating  the 
clear  solution  until  it  crystallises. 

I  have  found  by  experiment  that  a  solution  of  potassic 
cyanide  will  dissolve  only  about  one  half  as  much  cyanide 
of  zinc  as  of  cyanide  of  copper.  Zinc  oxide  dissolves 
somewhat  freely  in  a  boiling  solution  of  cyanide  of  potassium. 
Cyanide  of  zinc  dissolves  freely  in  a  solution  of  sesqui- 
carbonate  of  ammonium.  Ferro-cyanide  of  zinc  is  but  feebly 
soluble  in  a  boiling  solution,  either  of  ferro-cyanide  (yellow 
prussiate),  or  of  ferrid-cyanide  (red  prussiate)  of  potassium, 
but  dissolves  freely  in  a  boiling  solution  of  potassic  cyanide. 
Zinc  deposits  spread  over  black-leaded  surfaces  by  the  bat- 
tery process,  in  the  same  manner  as  copper. 

Deposition  of  zinc  by  simple  immersion  (see  p.  79). — Zinc 
is  too  electro-positive  a  metal  to  be  readily  set  free  by 
the  simple  immersion  process,  except  by  means  of  metals 
more  electro-positive  than  itself,  such  as  magnesium.  Silicon 
separates  zinc  from  its  fluoride  :  I  heated  together  1*5  grains 
of  crystals  of  silicon,  and  10-25  °f  perfectly  dry  fluoride  of 
zinc,  in  a  porcelain  crucible  to  a  red  heat.  Chemical  action 
occurred  throughout  the  mass,  and  vapour  of  zinc  escaped  ; 
some  of  the  zinc  remained  in  the  solid  state  on  cooling,  and 
evolved  bubbles  of  hydrogen  on  adding  dilute  hydrochloric 
acid.  According  to  A.  Cossa,  aluminium  separates  metallic 
zinc  from  an  alkaline  solution  of  zinc  (Watts,  '  Dictionary  of 
Chemistry,'  vol.  v.  p.  54).  From  a  solution  of  the  sulphate, 
magnesium  deposits,  with  energetic  action,  a  mixture  of  zinc, 
the  hydrated  oxide,  and  subsulphate  (Commaille,  '  Chemical 
News,'  vol.  xiv.  p.  188).  From  slightly  acid  solutions  of  salts 
of  zinc,  magnesium  deposits  the  pure  metal,  and  hydrogen 
gas  (Roussin,  'Chemical  News,'  vol.  xiv.  p.  27). 

V.  Roque  coats  articles  of  wrought  and  cast  iron  with 
zinc,  in  the  following  manner  : — Mix  together  1,000  measures 
of  water,  550  of  hydrochloric  acid,  fifty  of  sulphuric  acid, 
and  twenty  of  glycerine.  Clean  the  iron  in  this  mixture, 
and  place  it  in  a  solution  of  one  part  of  carbonate  of  potas- 

T  2 


2/6  The  Art  of  Electro-Metallurgy. 

sium  and  ten  of  water.  Then  immerse  it  during  from  three 
to  twelve  hours  (according  to  the  thickness  of  the  coating 
required),  in  a  mixture  composed  of  1,000  parts  of  water,  ten 
of  chloride  of  aluminium,  eight  of  bitartrate  of  potassium, 
five  of  chloride  of  tin,  four  of  chloride  of  zinc,  and  four  of 
acid  sulphate  of  aluminium  ('  Chemical  News/  vol.  xxi.  p. 
288). 

Depositing  zinc  by  contact  with  a  second  metal  (see  p.  83). — 
Raoult  states  that  gold  or  copper  in  contact  with  zinc,  in  a 
concentrated  and  boiling  solution,  of  chloride  or  sulphate  of 
zinc  (but  not  in  the  nitrate),  acquires  a  metallic  deposit.  But 
gold  in  contact  with  iron,  nickel,  antimony,  lead,  copper,  or 
silver,  in  cold  or  boiling,  acid  or  neutral,  solutions  of  salts 
of  zinc,  receives  no  such  coating  ('  Chemical  News,'  vol.  xxvi. 
p.  240;  vol.  xxvii.  p.  59;  'Journal  of  the  Chemical  So- 
ciety/ vol.  xi.  p.  464). 

Articles  of  copper,  or  brass,  cleaned  with  hydrochloric 
acid,  and  immersed  in  contact  with  zinc,  in  a  boiling  saturated 
solution  of  salammoniac,  or  chloride  of  zinc,  acquire  in 
a  few  minutes,  a  specular  covering  of  metal;  but  in  a  solution 
of  cream  of  tartar,  no  such  deposit  occurs  (R.  Bottger, 
'Gmelin's  Handbook  of  Chemistry/ vol.  i.  p.  501).  An- 
other  process  is  as  follows  : — Powdered  zinc  is  added  to  a 
concentrated  solution  of  salammoniac,  and  the  liquid  heated 
to  boiling.  The  articles  of  copper  or  brass  to  be  coated,  are 
placed  in  the  hot  liquid  in  contact  with  zinc,  and  become 
covered  with  a  brilliantly-white  layer  of  adherent  metal 
(Dr.  R.  Bottger,  «  Chemical  News/  vol.  xxii.  p.  108).  F.  Weil 
coats  copper,  or  coppered  metals,  with  zinc,  by  immersing 
them  in  a  concentrated  solution  of  potash  or  soda  (heated 
to  100°  C.),  in  contact  with  metallic  zinc.  The  deposit  is 
fixed  and  brilliant  ('  Chemical  News/  vol.  xiii.  p.  2). 

Deposition  of  zinc  by  means  of  a  separate  current  (see  p. 
89). — Zinc  may  be  deposited  from  its  sulphate,  ammonio- 
sulphate,  chloride,  ammonio-chloride,  acetate,  tartrate,  &c.,  by 
the  separate  current  process.  As  with  nearly  all  other  metals, 


Deposition  of  Zinc  by  a  Separate  Current.     277 

the  nitrate  forms  a  bad  depositing  solution.  By  proper  man- 
agement, good  coherent  metal  may  be  obtained  from  the 
sulphate,  acetate,  and  chloride.  A  solution  of  zinc  in 
caustic  potash  is  not  a  good  conductor  •  a  zinc  anode  does 
not  readily  dissolve  in  it ;  similarly  with  the  potassio-tartrate, 
and  potassio-cyanide  (Smee).  A  solution  of  one  part  of  the 
sulphate  in  five  to  ten  of  water,  with  a  large  zinc  anode, 
may  be  made  to  yield  a  good  deposit,  by  a  current  from  two 
small  Smee's  cells  feebly  charged. 

Many  years  ago,  sheets  and  other  articles  of  iron,  were 
coated  with  zinc  by  electrolysis,  in  order  to  protect  them 
from  rusting  ;  but  this  process  has  been  entirely  superseded 
by  the  so-called  '  galvanising,'  which  is  not  a  galvanic  pro- 
cess at  all,  but  consists  of  dipping  the  previously  cleaned 
iron  into  a  bath  of  melted  zinc  ;  the  latter  being  covered 
with  a  layer  of  saline  flux,  in  order  to  prevent  oxidation,  and 
also  to  dissolve  any  trace  of  oxide  which  may  be  upon  the 
iron  articles.  Such  a  coating  of  zinc  is  a  much  more  effectual 
preventive  of  rusting  than  an  electro-deposited  one,  because 
the  heat  expels  all  moisture  from  the  pores  of  the  iron,  and 
the  layer  of  zinc  is  homogeneous  and  not  granular  or  porous, 
whilst  that  formed  by  voltaic  action  is  always  more  or  less 
porous  and  very  liable  to  contain  traces  of  the  depositing 
liquid ;  the  surface  beneath  the  electro-deposit,  not  having 
been  heated  before  receiving  the  coating,  is  also  liable  to 
contain  moisture  and  acid,  absorbed  during  the  preparatory 
processes  of  cleaning,  &c. 

Alexander  Watt  patented,  in  the  year  1855,  a  process  by 
means  of  which  'tough  reguline  '  zinc  might  be  deposited. 
He  first  makes  a  mixture,  composed  of  twenty  gallons  of 
distilled  water,  200  ounces  of  cyanide  of  potassium,  and 
eighty  by  measure  of  the  strongest  aqueous  ammonia.  He 
then  fills  several  large  porous  cells,  with  a  solution  composed 
of  sixteen  ounces  of  cyanide  of  potassium  to  each  gallon  of 
water,  and  partly  immerses  them  in  the  other  liquid.  In  the 
porous  cells,  he  places  sheets  of  copper  or  iron  to  act  as 


278  The  A  rt  of  Electro-Metallurgy. 

cathodes,  and  in  the  outer  liquid,  clean  pieces  of  zinc  to  act 
as  anodes,  and  connects  the  battery  in  the  usual  way,  until 
about  sixty  ounces  of  zinc  are  dissolved,  and  then  stops  the 
current  and  removes  the  porous  vessels.  He  next  dissolves 
eighty  ounces  of  carbonate  of  potassium  in  a  part  of  the  zinc 
solution,  and  returns  it  to  the  original  portion,  and  stirs  the 
mixture  thoroughly.  After  the  sediment  formed  has  subsided, 
he  decants  the  clear  liquid  for  use.  Articles  of  iron  may  be 
coated  in  this  liquid.  Anodes  of  zinc  are  employed,  and  a 
little  cyanide  of  potassium,  and  liquid  ammonia,  are  occasion- 
ally added,  if  necessary.  The  battery  preferred,  is  composed 
of  two  Bunsen's  cells. 

MM.  Person  and  Sire  employ  a  mixture  composed  of 
one  part  of  oxide  of  zinc,  dissolved  in  100  of  water  containing 
ten  of  alum,  at  a  temperature  of  15°  C.  They  use  a  single 
battery  cell,  and  an  anode  of  the  same  amount  of  surface  as 
that  of  the  articles.  '  The  deposition  proceeds  as  easily  as 
that  of  copper,  and  takes  place  indifferently  on  any  metal — 
on  platinum  as  well  as  upon  copper  and  iron '  ('  Chemical 
News,'  vol.  ii.  p.  275). 

Estimation  of  zinc  by  means  of  the  battery. — J.  M.  Merrick 
electrolysed  known  weights  of  pure  double  sulphate  of  zinc 
and  ammonium,  in  aqueous  solution,  in  a  covered  platinum 
crucible,  with  a  platinum  wire  for  the  anode,  and  the  crucible 
for  the  cathode  (using  a  current  from  two  or  three  Grove's 
cells),  until  all  the  metal  was  deposited  ;  and  then  weighed 
the  deposit.  In  two  analyses,  16-16  and  16-31  per  cent  of 
zinc  was  obtained ;  theory  requiring  i6'2o  per  cent.  The 
deposits  were  washed  with  alcohol,  and  cautiously  dried 
('Chemical  News/  vol.  xxiv.  pp.  100,  172). 

Electro-deposition  of  alloys  of  copper  and  zinc. — There  are 
various  solutions  for  depositing  brass.  As  early  as  the  year 
1841,  M.  de  Ruolz  deposited  it  by  the  battery  process,  from 
the  mixed  cyanides  of  zinc  and  copper,  dissolved  in  a  solu- 
tion of  cyanide  of  potassium.  Whenever  zinc  is  electro- 
deposited  upon  perfectly  clean  copper,  the  first  film  deposited, 


Deposition  of  Brass.  279 

produces  a  yellow  colour,  by  uniting  with  the  copper.  In 
accordance  with-  this,  copper  articles  may  be  superficially 
brassed,  by  immersing  them  either  in  a  boiling  solution  of  bi- 
tartrate  of  potassium,  containing  zinc  amalgam,  or  in  the  same 
liquid,  after  some  dilute  hydrochloric  acid  has  been  added  to 
it.  Thicker  coatings  may  be  formed  upon  articles,  by  de- 
positing upon  them,  alternate  thin  films  of  zinc  and  copper, 
by  the  separate  current  method.  Processes  have  also  been 
patented,  for  coating  iron  and  steel  with  brass,  by  depositing  a 
layer  of  copper,  and  then  one  of  zinc,  upon  them,  and  heat- 
ing them  until  the  two  metals  more  perfectly  alloy  with  each 
other  (see  MM.  Person  and  Sire's  process,  '  Chemical  News/ 
vol.  ii.  p.  275). 

A  good  solution  for  brassing  by  means  of  a  separate 
current,  with  an  anode  of  brass,  may  be  made  by  dissolving 
nine  or  ten  ounces  of  the  strongest  aqueous  ammonia,  six- 
teen to  twenty  of  cyanide  of  potassium  (with  or  without  the 
addition  of  twenty  of  the  strongest  aqueous  hydrocyanic 
acid,  'Scheele's  strength,')  in  160  (i.e.  one  gallon)  of  water, 
and  saturating  the  hot  liquid  with  brass  by  means  of  an 
electric  current ;  it  must  be  used  at  2 1 2°  Fahr. 

Brunei,  Bisson,  and  Gaugain's  formula,  for  an  electro- 
brassing  solution,  consists  of  fifty  parts  of  carbonate  of  potas- 
sium, two  of  chloride  of  copper,  four  of  sulphate  of  zinc,  and 
twenty-five  of  nitrate  of  ammonium,  dissolved  together  in 
200  parts  of  cold  water,  and  used  with  a  brass  anode,  and 
a  strong  battery.  They  also  give  a  second  formula,  viz.  : — 
Take  twelve  and  a  half  gallons  of  water,  and  dissolve  in  it,  ten 
ounces  of  chloride  of  copper,  twenty  of  sulphate  of  zinc, 
twenty- four  of  cyanide  of  potassium,  and  160  of  carbonate 
of  potassium  ;  add  the  cyanide  the  last. 

Salzede's  patent,  dated  September  30,  1847  : — To  form 
the  solution,  take  5,000  parts  of  water,  dissolve  twelve  parts 
of  cyanide  -of  potassium  in  120  parts  of  it,  then  add  610 
of  carbonate  of  potassium,  forty-eight  of  sulphate  of  zinc,  and 
twenty-five  of  chloride  of  copper,  to  the  remainder  of  the 


2  8o  The  A  rt  of  Electro-Metallurgy. 

water,  and  heat  the  mixture  from  144°  to  172°  Fahr.  ;  and 
when  the  salts  are  entirely  dissolved,  add  305  parts  of  nitrate 
of  ammonium,  allow  the  liquid  to  remain  undisturbed  for 
twenty  hours,  and  then  add  the  solution  of  cyanide  of  potas- 
sium ;  allow  it  to  remain  again  till  clear,  and  then  draw  off 
the  transparent  liquid,  which  is  ready  for  use  ;  work  the  solu- 
tion with  a  large  brass  anode  and  a  strong  battery.  Another 
liquid  which  he  uses  for  brassing,  consists  of  5,000  parts  of 
water,  500  of  carbonate  of  potassium,  thirty-five  of  sulphate 
of  zinc,  fifteen  of  chloride  of  copper,  and  fifty  of  cyanide 
of  potassium. 

Russell  and  Woolrich's  patent,  dated  March  19,  1849  : — 
Take  ten  pounds  of  acetate  of  copper,  one  of  acetate  of  zinc, 
ten  of  acetate  of  potassium,  and  five  gallons  of  hot  water; 
dissolve  the  salts  in  the  water,  add  as  much  of  a  solution  of 
cyanide  of  potassium  as  will  precipitate  the  mixture  and  just 
re-dissolve  the  precipitate;  and  then  add  about  one-tenth 
more  of  the  cyanide.  Use  a  brass  anode,  or  else  two  anodes, 
one  of  zinc  and  one  of  copper. 

Joseph  Steele's  patent,  dated  August  9,  1850  : — Dissolve 
two  and  a  quarter  pounds  of  American  potash  in  six  gallons 
of  hot  water,  and  filter  the  solution  ;  also  dissolve  two  and  a 
half  ounces  of  acetate  of  copper  in  half  a  pint  of  strong 
liquid  ammonia,  and  add  it  to  the  first  liquid,  with  stirring ; 
then  add  four  or  five  ounces  of  sulphate  of  zinc,  and  stir  till 
dissolved  ;  and  finally  add  two  ounces  of  cyanide  of  potas- 
sium ;  filter  the  resulting  solution,  and  use  it  at  100°  Fahr., 
with  a  brass  anode.  To  obtain  a  dark -coloured  brass,  add 
more  acetate  of  copper ;  and  to  obtain  it  of  a  lighter  colour, 
add  more  sulphate  of  zinc. 

Mr.  Wood's  solution  is  composed  thus: — Dissolve  one 
pound  (troy  weight)  of  cyanide  of  potassium,  two  ounces  of 
cyanide  of  copper,  and  one  of  cyanide  of  zinc,  in  one  gallon 
of  distilled  water,  and  add  two  ounces  of  salammoniac. 
For  coating  smooth  articles,  use  the  solution  at  160°  Fahr. 


Deposition  of  Brass.  281 

with  a  battery  of  from  three  to  twelve  Grove's  cells.  It  is 
suitable  for  coating  iron  ('  Scientific  American  '). 

Mr.  Watt  gives  the  following  formula  for  a  brassing  liquid : 
— Acetate  of  copper  five  parts,  cyanide  of  potassium  eight, 
sulphate  of  zinc  ten,  liquid  ammonia  forty,  and  caustic  potash 
seventy-two  parts.  Reduce  the  copper  salt  to  powder,  and 
dissolve  it  in  eighty  parts  of  water ;  then  add  twenty  of 
the  aqueous  ammonia.  Dissolve  the  zinc  salt  in  1 60  parts 
of  water  at  180°  Fahr.,  add  the  remaining  twenty  of 
ammonia  to  it,  and  stir  the  mixture  strongly.  Dissolve 
the  potash  in  160  parts  of  water,  and  the  cyanide  in  160 
of  hot  water.  Add  the  solution  of  copper  to  that  of  zinc, 
then  add  the  caustic  potash,  and  then  the  cyanide.  Dilute 
the  mixture  to  eight  gallons  by  addition  of  water,  and 
thoroughly  stir  the  solution.  Use  a  strong  battery,  add  a 
little  ammonia  occasionally,  and  when  it  works  slowly,  add 
cyanide.  Keep  the  brass  anode  clean. 

According  to  Dr.  Heeren,  a  brassing  solution  may  be 
formed,  by  taking  a  mixture  containing  a  great  excess  of 
zinc  and  very  little  copper,  thus  : — Dissolve  one  part  of 
sulphate  of  copper,  eight  of  sulphate  of  zinc,  and  eighteen 
of  cyanide  of  potassium,  in  separate  portions  of  warm  water. 
Mix  the  copper  and  zinc  solutions,  then  add  the  dissolved 
cyanide  and  a  further  quantity  of  250  parts  of  distilled  water, 
and  stir  the  mixture.  The  bath  is  used  at  a  boiling  tempera- 
ture, with  a  current  from  two  Bunsen's  cells.  Very  rapid 
deposits  of  brass  have  been  thus  obtained  upon  articles  of 
copper,  zinc,  brass,  and  Britannia-metal  ('The  Chemist,' 
No.  16,  January  1855,  New  Series,  p.  342). 

Morris  and  Johnson's  patent,  dated  December  u,  1852. 
According  to  this,  dissolve  one  pound  of  cyanide  of  potas- 
sium, one  of  commercial  carbonate  of  ammonium,  two  ounces 
of  cyanide  of  copper,  and  one  of  cyanide  of  zinc,  in  a 
gallon  of  water,  and  use  the  solution  at  150°  Fahr.  with  a 
large  anode  of  brass  and  a  powerful  battery.  Or  a  solution 


282  The  A  rt  of  Electro-Metallurgy. 

may  be  taken  of  one  pound  of  cyanide  of  potassium,  and 
one  of  carbonate  of  ammonium,  dissolved  in  one  gallon  of 
water,  and  saturated  with  copper  and  zinc  to  the  requisite 
degree  by  means  of  a  strong  current,  a  large  brass  anode  and 
a  small  cathode,  until  the  latter  receives  a  good  deposit  of 
brass,  the  liquid  being  at  a  temperature  of  150°  Fahr.  To 
increase  the  proportion  of  copper  in  the  deposit,  either  add 
cyanide  of  potassium,  or  raise  the  temperature  of  the  liquid  ; 
and  to  increase  that  of  zinc,  either  add  carbonate  of  am- 
monium, or  lower  the  temperature. 

Roseleur  gives  the  following  recipes  for  making  brassing 
solutions.  No.  i. — Dissolve  in  1,000  parts  of  water,  twenty- 
five  of  sulphate  of  copper,  and  twenty-five  to  thirty  of  sul- 
phate of  zinc  ;  or  twelve  and  a  half  of  acetate  of  copper,  and 
twelve  and  a  half  to  fifteen  of  fused  chloride  of  zinc.  Pre- 
cipitate the  mixture,  by  means  of  100  parts  of  carbonate  of 
sodium  dissolved  in  plenty  of  water,  and  stir  the  mixture. 
Wash  the  precipitate  several  times  by  adding  water  to  it, 
stirring,  allowing  the  precipitate  to  subside,  and  pouring  the 
clear  liquid  away.  Add  to  the  washed  precipitate,  a  solution 
composed  of  fifty  parts  of  bisulphite  of  sodium,  and  TOO 
of  carbonate  of  sodium,  dissolved  in  1,000  of  water,  and, 
whilst  stirring  with  a  wooden  rod,  add  a  strong  solution  of 
ordinary  cyanide  of  potassium,  until  the  precipitate  is  just 
all  re-dissolved.  Then  add  two  and  a  half  or  three  parts  of 
free  cyanide.  No.  2. — To  form  a  cold  bath  for  brassing 
all  metals,  dissolve  in  200  parts  of  water,  fifteen  of  cupric 
sulphate,  and  fifteen  of  sulphate  of  zinc,  and  then  add  a  solu- 
tion of  forty  parts  of  carbonate  of  sodium  dissolved  in  TOO  of 
water,  and  stir  the  mixture.  Allow  the  precipitate  to  subside, 
throw  away  the  clear  liquid,  and  wash  the  sediment  by  addi- 
tion of  water,  followed  by  subsidence,  and  decantation.  Add 
to  the  drained  and  wet  precipitate,  900  parts  of  water,  con- 
taining twenty  of  bisulphite  and  twenty  of  carbonate  of 
sodium  dissolved  in  it.  Dissolve  twenty  parts  of  cyanide 
of  potassium,  and  two-tenths  of  a  part  of  arsenious  acid 


Deposition  of  Brass  upon  Iron.  283 

(white  arsenic),  in  100  of  water,  and  add  it  to  the  previous 
liquid ;  this  decolourises  the  mixture,  and  completes  the 
brassing  solution.  The  arsenious  acid  causes  the  deposit  to 
be  bright,  but  if  added  in  too  large  a  quantity,  whitens  it ; 
this  latter  effect,  however,  soon  disappears  by  working  the 
liquid.  In  using  this  bath,  if  the  deposit  is  dull,  add  a  little 
of  the  arsenic  ;  if  it  looks  earthy  or  ochreous,  add  cyanide  ; 
if  too  red,  add  zinc  salt,  and  if  necessary  also  cyanide  ;  if 
too  white,  add  copper  and  cyanide  ;  if  its  action  is  very 
slow,  add  copper  and  zinc  salts,  and  if  necessary  also  cyanide. 
As  the  brass  is  deposited  faster  than  it  dissolves,  salts  of 
copper,  and  of  zinc,  with  cyanide,  must  be  added  occasion- 
ally. When  by  addition  of  these  substances,  the  specific 
gravity  of  the  solution  becomes  greater  than  1-091,  the  solu- 
tion must  be  diluted  with  water  to  a  sp.  gr.  not  below  1-036. 
No.  3. — For  coating  steel,  cast  iron,  wrought  iron,  and 
tin  : — Dissolve  two  parts  of  bisulphite  of  sodium,  five  of 
cyanide  of  potassium  (of  75  per  cent),  and  ten  of  carbonate 
of  sodium,  in  eighty  of  distilled  water ;  and  add  to  the  mix- 
ture, one  part  of  fused  chloride  of  zinc,  and  one  and  a  quarter 
parts  of  acetate  of  copper,  dissolved  in  twenty  of  water. 
No.  4. — For  coating  articles  of  zinc : — Dissolve  twenty 
parts  of  bisulphite  of  sodium,  and  100  of  cyanide  of  potas- 
sium (of  75  per  cent),  in  2,000  of  water  ;  and  dissolve 
thirty-five  parts  of  chloride  of  zinc,  thirty-five  of  acetate  of 
copper,  and  forty  of  aqueous  ammonia,  in  500  of  water ; 
mix  the  two  solutions,  and  filter  the  mixture.  Too  strong  a 
current  in  these  solutions  usually  makes  the  deposit  white, 
and  too  weak  a  one,  or  keeping  the  articles  in  motion, 
makes  it  red.  The  proportion  of  zinc  in  the  baths  may  be 
increased  by  using  a  zinc  anode,  and  of  copper  by  employ- 
ing a  copper  one.  The  brass  anodes  may  be  kept  free  from 
undissolved  oxide  of  zinc,  by  adding  the  minimum  quantity 
of  ammonia;  but  that  must  not  be  added  to  cold  solu- 
tions used  for  brassing  iron.  To  preserve  the  colour  of  the 
deposit,  rinse  the  coated  articles  in  water,  then  in  water 


284  The  A  rt  of  Electro-Metallurgy. 

made  slightly  alkaline  by  addition  of  caustic  lime,  and  then 
thoroughly  dry  them  in  a  stove. 

For  coating  cast  iron  with  brass,  Walenn  recommends  a 
bath,  composed  of  an  aqueous  solution  of  equal  parts  of 
ammonic-tartrate  and  potassic-cyanide.  After  addition  of 
cyanide  of  copper,  and  cyanide  of  zinc,  in  certain  propor- 
tions, the  oxides  of  the  metals  are  added  to  the  solution. 
If  upon  trial,  hydrogen  is  evolved  at  the  cathode,  a  little 
ammoniuret  of  copper  is  added  to  the  cold  bath.  The 
temperature  at  which  this  liquid  is  used,  determines  the  colour 
of  the  brass,  and  may  vary  from  60°  C.  to  nearly  the  boiling 
point  ('  Chemical  News,'  vol.  xxi.  p.  273).  He  also  makes 
the  following  remarks  on  the  electro-deposition  of  copper 
and  brass.  '  A  solution  containing  one  pound  of  cupric 
sulphate,  and  one  of  sulphuric  acid,  to  a  gallon  of  water, 
deposits  the  metal  in  a  solid  compact  mass,  with,  a  somewhat 
botryoidal  surface.  The  addition  of  one  ounce  of  zinc  sul- 
phate (as  recommended  by  Napier)  prevents  this  botryoidal 
form,  and  renders  the  deposit  tough,  compact,  and  even. 
From  a  solution  containing  a  greater  proportion  of  zinc 
sulphate,  the  copper  is  deposited  in  tufts  of  needles  standing 
at  right  angles  to  the  surface  of  the  metal.  Ordinary  electro- 
brassing  liquids  show  the  same  peculiarity  in  even  a  more 
marked  degree,  and  this  makes  it  impossible  to  produce  a 
good  deposit  of  more  than  -01  to  -03  inch  in  thickness.  This 
form  of  deposit  is  owing  chiefly  to  a  copious  evolution  of 
hydrogen  taking  place  during  its  formation.'  However  the 
author  has  found,  that  by  employing  a  solution  containing  both 
the  oxides  and  the  cyanides  of  the  two  metals,  together  with 
some  neutral  tartrate  of  ammonium,  this  evolution  of  hydro- 
gen may  usually  be  avoided,  or,  should  it,  nevertheless,  take 
place  to  a  slight  extent,  it  may  be  entirely  stopped  by  the 
addition  of  some  cupric  ammonide.  Such  a  solution  yields 
brass  of  a  uniform  character,  and  the  deposit,  which  may  be 
obtained  of  any  desired  thickness,  is  tough,  and  has  a  com- 
pact, even  texture.  As  there  is  no  evolution  of  hydrogen, 


Deposition  of  German- Silver.  285 

no  electric  force  is  wasted,  and  perfect  results  may  be  ob- 
tained with  a  single  Wollaston's  or  Smee's  cell  ;  but  in  prac- 
tice a  little  stronger  current  than  this  is  employed,  in  order 
to  hasten  the  process  ('  Philosophical  Magazine,'  4th  Series, 
vol.  xli.  p.  41  ;  'Chemical  News,'  vol.  xxii.  pp.  i,  181  ; 

*  Journal  of  the  Chemical  Society,'  vol.  x.  p.  103). 

Deposition  of  other  alloys  of  zinc. — Watt  states  that  he  has 

*  succeeded  in  depositing  an  alloy  of  copper,  zinc,  and  nickel, 
forming  a  very  good  quality  of  german-silver,  by  dissolving 
german-silver  in  nitric  acid,  precipitating  with  an  alkali,  and 
re-dissolving  with  cyanide  of  potassium '  ('  Electro-Metal- 
lurgy,' by  A.  Watt ;  Weale's  <  Elementary  Series,'  p.  91). 

Newton  patented  (July  29,  1850)  a  solution  for  depositing 
an  alloy  of  copper,  tin,  and  zinc  ;  it  consisted  of  the  double 
cyanide  of  copper  and  potassium,  in  combination  with 

*  zincate '  and  stannate  of  potassium,  '  or  the  double  tartrates 
of  the  metals  and  potassium,  may  be  used.' 

Messrs.  Morris  and  Johnson  (according  to  their  patent), 
deposit  german-silver  by  the  following  process : — Dissolve 
one  pound  of  cyanide  of  potassium,  and  one  of  carbon- 
ate of  ammonium,  in  a  gallon  of  water,  heat  the  solution 
to  150°  Fahr.,  immerse  a  large  anode  of  german-silver  in  the 
liquid,  and  a  small  cathode  of  any  suitable  metal,  connect 
the  two  with  a  powerful  battery,  and  pass  the  current  of 
electricity  until  a  considerable  amount  of  metal  is  dissolved, 
and  a  bright  cathode  receives  a  deposit  of  good  colour  ;  the 
solution  is  then  ready  for  use.  If  the  deposit  becomes  too 
red,  add  carbonate  of  ammonium  ;  if  too  white,  add  cyanide. 

Separation  of  copper  and  zinc  by  electro-deposition. — Ac- 
cording to  M.  Hautefeuille,  the  oxides  of  copper  and  zinc, 
dissolved  in  aqueous  ammonia,  may  be  separated  by  the 
following  process  : — Add  an  excess  of  acetic  acid  to  the 
solution,  immerse  a  clean  sheet  of  lead,  and  boil  the  mixture 
two  hours,  or  until  it  becomes  quite  colourless  ;  the  whole  of 
the  copper  is  then  precipitated  in  the  metallic  state  ('  The 
Chemist,'  New  Series,  part  xviii.,  March  1855,  p.  334). 


286  The  A  rt  of  Electro-Metallurgy. 


CLASS  V.  EARTH  AND  ALKALINE  EARTH 
METALS. 

MAGNESIUM — CERIUM — LANTHANUM — DIDYMIUM — GALLIUM 
—  ALUMINIUM  —  GLUCINIUM  —  CALCIUM  —  STRONTIUM  — 
BARIUM. 

31.  Magnesium.— Elec.-chem.  eqt.=-^^-=i2-i5.    The 

ordinary  salts  of  this  metal  are  the  oxide  (calcined  magnesia), 
the  nitrate,  chloride,  carbonate,  and  sulphate;  the  most  fre- 
quent impurity  in  them  is  lime.  As  the  metallic  magne- 
sium of  commerce  is  free  from  calcium,  and  very  pure,  extra 
pure  salts  of  the  metal  may  be  made  by  means  of  it.  The 
nitrate,  chloride,  and  sulphate,  may  be  made  by  saturating 
the  corresponding  diluted  acids,  with  the  metal,  the  oxide, 
or  carbonate,  and  evaporating  the  solutions.  In  evaporating 
a  solution  of  the  chloride  to  dryness,  towards  the  end  of  the 
operation,  some  of  the  salt  is  decomposed  by  the  watery 
vapour,  hydrochloric  acid  being  formed,  and  oxide  of  mag- 
nesium left ;  and  to  obviate  this,  a  portion  of  salammoniac 
is  added  when  the  solution  has  become  very  concentrated. 

Magnesium  is  highly  electro-positive ;  it  precipitates  as 
metal,  from  solutions  of  their  salts,  bismuth,  platinum,  gold, 
silver,  mercury,  copper,  lead,  thallium,  tin,  and  cadmium 
(Roussin,  'Chemical  News,'  vol.  xiv.  p.  27).  According  to 
Phipson,  magnesium  deposits  nearly  all  metals  from  their 
neutral  solutions  (even  iron  and  manganese  from  ferrous  and 
manganous  salts)  in  the  metallic  state.  It  deposits  platinum, 
gold,  silver,  bismuth,  mercury,  copper,  nickel,  cobalt,  iron, 
lead,  thallium,  tin,  cadmium,  and  zinc,  but  not  aluminium 
(Watts,  '  Dictionary  of  Chemistry,'  vol.  v.  p.  795). 

I  melted  to  a  perfect  liquid,  at  nearly  a  white  heat,  a 
mixture  of  six  grains  of  magnesic  fluoride,  and  four  of  calcic 
fluoride;  then  added  two  grains  of  crystals  of  silicon,  the 


Deposition  of  Magnesium.  287 

crystals  were  not  dissolved,  and  there  appeared  no  signs  of 
metallic  magnesium  having  been  separated. 

Electrolysis  of  salts  of  magnesium. — When  moistened 
sulphate  of  magnesium  is  formed  into  a  cup  upon  a  platinum 
plate,  the  cup  filled  with  mercury  and  made  the  cathode, 
and  the  platinum  the  anode,  with  a  current  from  a  powerful 
battery,  magnesium  is  deposited  into  the  mercury. 

Bunsen  electrolysed  fused  chloride  of  magnesium,  at  a  red 
heat,  in  a  deep  and  covered  porcelain  crucible,  divided  by  a 
vertical  partition  of  porous  porcelain,  which  extended  half- 
way down  the  vessel.  The  electrodes  were  of  carbon,  and  in- 
troduced through  openings  in  the  cover  ;  and  the  current  was 
from  ten  cells  of  a  zinc  and  carbon  battery.  As  magnesium 
is  a  light  metal,  it  would  rise  to  the  surface  of  the  mixture 
and  burn  in  the  air  ;  and,  in  order  to  prevent  this  as  much 
as  possible,  the  cathode  was  notched  (see  fig.  28),  so  that 
the  melted  metal  collected  in  the  notches.  According  to 
Matthiessen,  a  fused  mixture,  in  the  proportions  of  four 

FIG.  28. 


molecules  of  magnesic,  and  three  of  potassic  chloride,  forms 
a  much  better  electrolyte,  because  the  magnesium  sinks  in 
it.  '  A  solution  of  the  chloride  of  sodium  or  ammonium, 
electrolysed  with  electrodes  of  magnesium  wire,  deposits  a 
black  powder  of  suboxide  of  magnesium  upon  the  anodes 
(W.  Beetz, '  Watts'  Chemical  Dictionary/  Supplement,  p.  796) 


288  The  Art  of  Electro-Metallurgy. 

According  to  M.  A.  Bertrand,  a  strong  current  deposits 
magnesium  in  a  few  minutes  upon  a  sheet  of  copper,  in  an 
aqueous  solution  of  the  double  chloride  of  magnesium  and 
ammonium.  The  deposit  is  homogeneous,  strongly  adherent, 
and  polishes  readily  ('  Chemical  News,'  vol.  xxxiv.  p.  227). 

32.  Cerium,  lanthanum,  and  didymium. — To  deposit 
either  of  these  metals,  its  chloride  is  mixed  with  salammoniac 
(both  as  dry  as  possible),  and  the  mixture  heated  to  redness  in 
a  platinum  crucible  to  expel  all  the  salammoniac.     A  porous 
clay  vessel,  of  the  best  quality,  is  filled  with  the  residue,  then 
placed  in  a  Hessian  crucible,  surrounded  by  a  cylinder  of 
sheet  iron  (with  a  long  projecting  strip  for  connexion),  to 
serve  as  the  anode,  and  the  space  between  the  two  vessels 
filled  with  a  previously  melted  mixture  of  an  equal  number 
of  equivalents   of  the  chlorides  of  potassium  and  sodium. 
A  thick  iron  wire,  enclosed  in  a  clay  pipe,  has  a  coil  of  very 
fine  iron  wire  at  its  extremity  to  serve  as  the  cathode,  and  is 
immersed  in  the  fused  salt  in  the  inner  vessel.     The  fusion 
is  effected  by  preference  in  a  fire  of  glowing  charcoal,  to 
prevent  as  far  as  possible  the  presence  of  aqueous  vapour, 
and  a  strong  current  is  employed  (Bunsen, '  Electrical  News/ 
vol.  i.  p.  184). 

33.  Gallium, — Gallium  is  allied  to  aluminium.     It  melts 
easily  (at  29-5°  C.),  when  held  between  one's  fingers ;  but 
does  not  easily  volatilise  or  oxidise,  even  when  heated  to 
bright  redness.     Liquid  gallium  is  whiter  than  mercury  ;  the 
solid  metal  is   hard,  and  somewhat   malleable,  of  specific 
gravity  4*7,  not  oxidised  by  cold  nitric  acid,  but  dissolves  in 
cold  dilute  hydrochloric  or  hot  nitric  acid    The  oxide  of 
this  rnetal  is  not  very  soluble  in  aqueous  ammonia,  but  a 
solution  of  caustic  potash  dissolves  a  large  quantity  of  it. 
The  metal  has  been  obtained  by  the  electrolysis  of  both  these 
solutions,  formed  by  adding  an  excess  of  those  alkalies  to 
the  sulphate  of  gallium.     It  is  deposited  upon  the  platinum 
cathode  as  a  dead,  whitish-grey  coating,  formed  of  minute 
globules  like  mercury  ('  Chemical  News,'  vol.  xxxiii.  p.  193). 


Deposition  of  Aluminium.  289 

34.  Aluminium. — Elec.  chem.  eqt.  =  2-L5.s=  9-16.  The 

o 

oxide  (alumina),  chloride,  sulphate,  alumand  (a  double  sul- 
phate of  aluminium  and  an  alkaline  metal,  usually  ammo- 
nium, or  potassium)  are  its  most  common  salts  ;  the  chloride 
sulphate,  and  alum,  are  freely  soluble  in  water. 

Magnesium  does  not  deposit  aluminium  as  metal  from 
its  solutions  (Roussin,  *  Chemical  News/  vol.  xiv.  p.  27). 

Electrolysis  of  salts  of  aluminium. — With  regard  to  the 
separation  of  aluminium  by  means  of  electrolysis,  M.  H. 
Sainte-Claire  Deville  says  : — *  It  appeared  to  me  impossible 
to  obtain  aluminium  by  the  battery  in  aqueous  liquids.  I 
should  believe  this  to  be  an  impossibility,  if  the  brilliant  ex- 
periments of  M.  Bims.en  on  the  production  of  barium,  did 
not  shake  my  conviction.  Still  I  may  say,  thai  all  processes 
of  this  description  which  have  recently  been  published  for  the 
preparation  of  aluminium,  have  failed  to  give  me  good  results. 
It  is  of  the  double  chloride  of  aluminium  and  sodium,  of 
which  I  have  already  spoken,  that  this  decomposition  is 
effected.  The  bath  is  composed  of  two  parts,  by  weight,  of 
chloride  of  aluminium,  with  the  addition  of  one  part  of  dry 
and  pulverised  common  salt.  The  whole  is  mixed  in  a 
porcelain  crucible,  heated  to  about  392°  Fahr.  The  com- 
bination is  effected  with  disengagement  of  heat,  and  a  liquid 
is  obtained  which  is  very  fluid  at  392°  Fahr.,  and  fixes  at 
that  temperature.  It  is  introduced  into  a  vessel  of  glazed 
porcelain,  which  is  to  be  kept  at  a  temperature  of  about 
392°  Fahr.  The  cathode  is  a  plate  of  platinum,  on  which 
the  aluminium  (mixed  with  common  salt)  is  deposited  in 
the  form  of  a  greyish  crust.  The  anode  is  formed  of  a 
cylinder  of  charcoal,  placed  in  a  perfectly  dry,  porous 
vessel,  containing  melted  chloride  of  aluminium  and  sodium. 
(The  densest  charcoal  rapidly  disintegrates  in  the  bath,  and 
becomes  pulverulent,  hence  the  necessity  of  the  porous 
vessel.)  The  chlorine  is  thus  removed,  with  a  little  chloride 
of  aluminium  proceeding  from  the  decomposition  of  the 


290  The  A  rt  of  Electro-Metallurgy. 

double  salt.  This  chloride  would  volatilise  and  be  entirely 
lost,  if  some  common  salt  were  not  in  the  porous  vessel. 
The  double  chloride  becomes  fixed,  and  the  vapours  cease. 
A  small  number  of  voltaic  elements  (two  are  all  that  are  ab- 
solutely necessary)  will  suffice  for  the  decomposition  of  the 
double  chloride,  which  presents  but  little  resistance  to  the 
electricity.  The  platinum  plate  is  removed  when  it  is  suffi- 
ciently charged  with  the  metallic  deposit.  It  is  suffered  to 
cool,  the  saline  mass  is  rapidly  broken  off,  and  the  plate  re- 
placed' ('The  Chemist,'  New  Series,  No.  13,  October 
1854,  p.  12). 

M.  Duvivier  states,  that  by  passing  an  electric  current 
from  eighty  Bunsen's  cells,  through  a  small  piece  of '  laminae 
disthene '  between  two  carbon  points,  the  disthene  melted 
entirely  after  two  or  three  minutes  ;  the  elements  which 
composed  it,  were  partly  disunited  by  the  power  of  the 
electric  current,  and  the  aluminium  freed  from  its  oxygen. 
Several  globules  of  the  metal  separated,  one  of  which  was 
as  white  and  as  hard  as  silver  ('  The  Chemist,'  New  Series, 
No.  xi.,  August  1854,  p.  687). 

Bunsen  electrolysed  fused  chloride  of  aluminium  and 
sodium,  by  a  similar  process  to  that  already  described  in  de- 
positing magnesium  (see  p.  287).  The  salt  fused  at  356°  C., 
and  readily  yielded  the  metal.  The  temperature  of  the  liquid 
should  be  raised  nearly  to  the  melting-point  of  silver ;  the 
particles  of  liberated  aluminium  then  fuse,  unite  together, 
and  form  globules,  which,  being  of  greater  specific  gravity 
than  the  salt,  fall  to  the  bottom  of  the  crucible.  I  electro- 
lysed a  strong  solution  of  pure  fluoride  of  aluminium,  con- 
taining free  hydrofluoric  acid,  using  the  platinum  containing 
vessel  as  the  cathode,  and  a  sheet  of  platinum  as  the  anode ; 
gas  was  evolved  freely  from  the  latter,  and  the  liquid  became 
heated. 

M.  Corbelli,  of  Florence,  deposits  aluminium,  by  electro- 
lysing a  mixture  of  rock-alum,  or  sulphate  of  aluminium,  and 
the  chlorides  of  calcium  or  of  sodium,  the  anode  being 


Deposition  of  Aluminium.  291 

formed  of  iron  wire,  coated  with  an  insulating  material,  and 
dipping  into  mercury  placed  at  the  bottom  of  the  solution  ; 
and  the  cathode  of  zinc  immersed  in  the  solution.  Alu- 
minium is  then  deposited  upon  the  zinc,  and  the  chlorine 
which  is  eliminated  at  the  anode,  unites  with  the  mercury, 
and  forms  calomel  (Watts,  '  Dictionary  of  Chemistry,'  vol.  i. 
p.  152). 

Thomas  and  Tilley  took  out  a  patent  Dec.  26,  1854,  for 
depositing  aluminium  from  a  solution,  composed  of  freshly 
precipitated  alumina,  dissolved  in  boiling  water  containing 
cyanide  of  potassium;  and  another,  Dec.  6,  1855,  for  de- 
positing it  from  a  solution  of  calcined  alum  in  aqueous 
cyanide  of  potassium  ;  also  from  several  other  liquids ;  and 
for  depositing  alloys  of  aluminium  and  silver;  aluminium, 
silver,  and  copper;  aluminium  and  tin  ;  aluminium,  silver, 
and  tin  ;  aluminium  and  copper ;  aluminium  and  nickel ; 
aluminium  and  iron,  &c. 

J.  B.  Thompson  states,  that  he  has  for  more  than  two 
years,  been  depositing  aluminium  on  iron,  steel,  and  other 
metals,  at  a  temperature  of  about  500°  Fahr.,  and  also  de- 
positing aluminium  bronze  of  various  tints,  from  the  palest 
yellow  to  the  richest  gold  colour  ('  Chemical  News/  vol. 
xxiv.  p.  194). 

Jeancon  patented  a  process,  for  depositing  aluminium 
from  an  aqueous  solution  of  a  double  salt  of  that  metal  and 
potassium,  of  sp.  gr.  1-161,  by  means  of  a  current  from  three 
Bunsen's  cells,  the  solution  being  at  140°  Fahr.  (<  Telegraphic 
Journal,'  vol.  i.  p.  308).  T.  Bell  also  patented  a  process,  for 
depositing  aluminium  upon  other  metals,  from  the  double 
chloride  of  that  metal  and  potassium  ('Chemical  News,' 
vol.  v.  p.  153).  M.  A,  Bertrand  states,  that  he  has  deposited 
aluminium  upon  a  plate  of  copper,  in  a  solution  of  the 
double  chloride  of  aluminium  and  ammonium,  by  employ- 
ing a  strong  current  ;  and  that  the  deposit  was  capable  of 
receiving  a  brilliant  polish  ('  Chemical  News,  vol.  xxxiv.  p. 
227). 

U  2 


292  The  A  rt  of  Electro-Metallurgy. 

According  to  C.  Winckler,  plating  with  aluminium  can- 
not be  effected  by  electro -deposition  (*  Chemical  News/  vol. 
xxvi.  p.  157;  'Journal  of  the  Chemical  Society,'  vol.  x. 
p.  1134).  Sprague  also  states  his  inability  to  deposit 
that  metal  (Sprague,  '  Electricity,'  p.  309). 

Aluminium  used  as  an  anode  in  electrolysing  dilute  sul 
phuric  acid,  stops  the  current ;  but  not  if  it  is  employed  as 
the  cathode  ('Telegraphic  Journal,'  vol.  iii.  p.  59 ;  '  Chemi- 
cal News/  vol.  xxxi.  p.  99). 

35.  Glucinium. — Elec.-chem.   eqt.  =-?-^-=  4-65.      The 

commonest  salts  of  this  metal,  are  the  carbonate  and  sul- 
phate ;  the  latter  is  freely  soluble  in  water  ;  the  nitrate  and 
chloride  are  also  very  soluble,  and  may  be  easily  made,  by 
adding  sufficient  of  the  carbonate  to  the  respective  acids, 
and  evaporating  the  solutions. 

Becquerel  deposited  the  pure  metal  from  a  concentrated 
solution  of  its  chloride  (by  means  of  a  current  from  twenty 
cells),  in  the  form  of  brilliant,  steel- grey,  crystalline  laminae 
(Gmelin's  '  Handbook  of  Chemistry/  vol.  iii.  p.  293). 

36.  Calcium. — Elec.-chem.  eqt.  =  —  =  20.     The  com- 
mon salts  of  calcium,  are  the  oxide  (caustic  lime),  the  nitrate, 
fluoride,   chloride,  bromide,  carbonate   (chalk   or  whiting), 
sulphate,  phosphate,  &c.     Ordinary  caustic  lime  is  often  im- 
pure ;  a  much  purer  kind  may  be  obtained,  by  heating  the 
pure  carbonate  to  full  redness ;  the  latter  may  be  obtained 
as  follows:  Add  an  excess  of  clear  lime-water  to  a  solu- 
tion of  nitrate  of  calcium  ;  filter  the  liquid,  and  precipitate 
it  with  a  mixture  of  ammonia  and  carbonate  of  ammonium, 
dissolved   in  water,  and  wash   the  precipitate  thoroughly. 
Pure  soluble  salts  of  lime  may  be  obtained,  by  neutralising 
the  respective  pure  acids  with  the  pure  carbonate,  and  eva- 
porating the  clear  solutions.   The  sulphate  of  calcium  is  only 
sparingly  soluble  in  water,  the  fluoride  and  phosphate  much 
less  so ;  caustic  lime  also  does  not  dissolve  very  freely. 


Deposition  of  Calcium.  293 

Electrolysis  of  salts  of  calcium. — Sir  H.  Davy  first  depo- 
sited impure  calcium  by  electrolysis  into  a  cathode  of  mer- 
cury during  the  year  1808;  and  since  that  period,  several 
other  investigators  have  effected  the  same  object,  by  means 
of  much  less  powerful  electric  currents. 

M.  Fremy  fused  pure  fluoride  of  calcium  in  a  platinum 
crucible,  and  electrolysed  it ;  a  brisk  effervescence  occurred 
in  the  mass,  and  a  gas  was  evolved  at  the  positive  pole,  which 
corroded  glass ;  metallic  calcium  was  deposited  upon  the 
cathode,  and  was  at  once  converted  into  lime  by  the  atmo- 
sphere. It  was  difficult  to  make  the  observations,  and  the 
crucible  was  soon  alloyed,  and  leaked,  and  the  melted  fluo- 
ride escaped  ('  The  Chemist/  New  Series,  vol.  ii.  p.  548). 

Matthiessen  melted  and  electrolysed  a  mixture,  in  the 
proportions  of  two  molecules  of  chloride -of  calcium,  and  one 
of  chloride  of  strontium,  with  a  small  quantity  of  sal  ammo- 
niac, in  a  porcelain  crucible,  with  an  anode  of  gas-carbon, 
and  a  cathode  formed  by  winding  a  thin  iron  wire  round  a 
thicker  one,  and  dipping  it  only  just  into  the  fused  mixture. 
The  calcium  was  deposited  in  beads  upon  the  fine  wire. 

Bunsen  electro-deposited  metallic  calcium,  in  a  similar 
manner  to  that  employed  for  manganese  and  chromium 
(see  pp.  250,  253),  except  that  the  density  of  the  current 
employed  was  greater.  He  acidulated  a  concentrated  and 
boiling  hot  solution  of  the  chloride,  with  hydrochloric  acid, 
poured  the  boiling  liquid  into  the  porous  cell,  and  employed 
as  a  cathode,  an  amalgamated  platinum  wire.  The  calcium 
was  deposited  as  a  grey  layer  upon  the  amalgamated  surface. 
The  process  is  difficult,  because  the  calcium  quickly  oxidizes 
to  a  layer  of  lime,  which  covers  the  cathode,  and  stops  the 
current.  The  deposit  must  be  frequently  removed,  and  the 
wire  freshly  amalgamated,  each  time  before  re-immersion  ; 
and  even  then  but  a  small  amount  of  the  metal  is  obtained 
('The  Chemist,'  New  Series,  vol.  i.  part  ii.,  August  1854, 
p.  686). 

Herschel  observed,  that  in  a  solution  of  chloride  of  cal- 


294  The  Art  of  Electro -Metallurgy. 

cium  undergoing  electrolysis,  the  cathode  evolved  gas,  and 
became  covered  with  caustic  hydrate  of  lime. 

37.  Strontium. — Elec.-chem.  eqt.=  ~U  =  4375.     The 

ordinary  salts  of  strontium,  are  the  nitrate,  chloride,  carbo- 
nate, and  sulphate  ;  the  two  former  are  freely  soluble  in 
water,  and  the  two  latter  insoluble. 

Silicon  does  not  separate  strontium  from  its  fluoride.  I 
heated  to  redness,  a  mixture  of  crystals  of  silicon  and  fluo- 
ride of  strontium  ;  the  crystals  suffered  no  loss  of  weight, 
did  not  appear  corroded,  and  no  signs  of  free  strontium 
were  obtained. 

Electrolysis  of  salts  of  strontium. — Sir  H.  Davy  first  de- 
posited this  metal  by  electrolysis,  in  the  year  1808,  by  forming 
into  a  cup,  a  pasty  mass  of  its  carbonate  with  water,  and 
placing  it  upon  a  platinum  dish  as  an  anode,  the  cup  being 
filled  with  mercury  to  act  as  the  cathode.  On  passing  a 
current  from  a  5oo-cell  battery  through  it,  the  strontium  was 
deposited  upon,  and  absorbed  by,  the  mercury. 

Bunsen  obtained  strontium,  in  a  precisely  similar  way  to 
that  of  obtaining  calcium  (p.  293),  using  a  salt  of  strontium 
instead  of  one  of  that  metal  (Watts,  '  Dictionary  of  Chem- 
istry,' vol.  ii.  p.  437).  Matthiessen  obtained  it  from  the 
fused  chloride  in  the  following  manner : — A  small  porous 
cell  was  placed  in  a  porcelain  crucible,  and  both  vessels 
nearly  filled  with  anhydrous  chloride  of  strontium,  the  level 
of  that  in  the  porous  cell  being  the  highest.  The  salt  was 
melted  so  that  a  crust  appeared  on  its  surface.  The  cathode 
consisted  of  a  thick  iron  wire,  enclosed  in  the  stem  of  a 
tobacco-pipe,  so  that  only  -^th  of  an  inch  of  it  projected  at 
the  lower  end,  round  which  a  very  thin  iron  wire  was  coiled. 
The  anode  was  a  cylinder  of  sheet  iron  placed  in  the  outer 
space.  The  cathode  was  immersed  in  the  inner  vessel,  and 
the  current  passed ;  the  metal  collected  upon  it  beneath  the 
crust  (Watts,  '  Dictionary  of  Chemistry,'  vol.  ii.  p.  438). 

Strontium  is  electro-negative  to  potassium  and  sodium  in 
water,  but  positive  to  magnesium. 


Deposition  of  Barium.  295 

38.  Barium.— Elect.-chem.  eqt.  =  H?  =68-5.      Its  or- 
dinary salts  are,  the  oxide,  hydrated   oxide  (both   termed 
caustic  baryta),  nitrate,  chloride,  carbonate,  and   sulphate. 
The  oxide,  nitrate,  and  chloride  are  soluble  in  water ;  the 
carbonate  and  sulphate  are  insoluble. 

Crookes  deposited  barium,  by  simple  immersion  of  an 
alloy  of  sodium  and  mercury  in  a  saturated  solution  of 
barium  chloride  at  93°  C.  The  deposited  metal  dissolved 
in  the  mercury,  and  formed  an  amalgam  ('Chemical  News,' 
vol.  vi.  p.  194  ;  Watts,  '  Dictionary  of  Chemistry,'  vol.  v. 

P-  252). 

Electrolysis  of  salts  of  barium. — Davy  first  deposited 
barium,  by  passing  a  powerful  electric  current  through  a 
concentrated  solution  of  hydrate  of  baryta,  into  a  cathode  of 
mercury ;  the  deposit  formed  an  amalgam  with  that  metal. 

Bunsen  obtained  barium,  by  electrolysis  of  a  boiling  hot, 
concentrated,  and  acidulated  solution  of  its  chloride,  in  a 
similar  manner  to  that  of  separating  calcium  (see  p.  293)  ;  it 
was  more  easily  obtained.  The  deposit  upon  the  mercurial 
surface  formed  an  amalgam,  which  was  silvery-white,  and 
very  crystalline  ('The  Chemist/  New  Series,  vol.  i.  p.  686  ; 
Watts,  '  Dictionary  of  Chemistry,'  vol.  i.  p.  500). 

Matthiessen  obtained  barium  from  its  chloride,  in  a 
similar  manner  to  that  in  which  he  deposited  strontium  (see 
p.  294). 

A  solution  of  nitrate  of  barium,  electrolysed  by  means  of 
platinum  electrodes,  yields  nitric  acid  at  the  anode,  and  baryta 
at  the  cathode  (Sir  H.  Davy). 

CLASS   VI.    ALKALI-METALS. 

LITHIUM — SODIUM — POTASSIUM — RUBIDIUM — CAESIUM — 
AMMONIUM. 

39.  Lithium. — Elec.-chem.  eqt.  =  7.   The  most  common 
salt  of  lithium,  is  the  carbonate,  and  from  this  the  other  salts 


296  The  A  rt  of  Electro-Metallurgy. 

may  be  easily  prepared,  by  adding  an  excess  of  it  to  the  par- . 
ticular  acid,  filtering  the  mixture,  and  crystallising  the  solu- 
tion.    All  the  salts  of  lithium  (except  the  phosphate),  formed 
by  adding  the  carbonate  to  the  common  mineral  acids,  are 
freely  soluble  in  water. 

I  added  crystals  of  silicon  to  a  fused  mixture  of  the  fluo- 
rides of  lithium  and  sodium,  but  the  silicon  was  not  corroded 
or  diminished  in  weight,  and  lithium  was  not  deposited. 

Electrolysis  of  salts  of  lithium. — Bun  sen  was  the  first 
person  who  electro-deposited  this  metal  (Watts,  '  Dictionary 
of  Chemistry,'  vol.  iii.  p.  727).  By  electrolysing  fused  chlo- 
ride of  lithium,  with  a  current  from  four  or  six  Bunsen's 
cells,  an  anode  of  gas-coke,  and  a  cathode  of  iron  wire,  he  de- 
posited silver- white  metal  upon  the  wire  (Watts'  '  Dictionary 
of  Chemistry,'  vol.  ii.  p.  437,  and  vol.  iii.  p.  727).  Schnitzler 
also  electrolysed  a  mixture  of  the  fused  chlorides  of  lithium 
and  ammonium,  with  a  current  from  twelve  Bunsen's  cells, 
and  a  cathode  of  iron  wire  ('Journal  of  the 
Chemical  Society,'  vol.  xii.  p.  961). 


I  fused  some  fluoride  of  lithium  in  an 
open  platinum  crucible,  within  a  partially 
covered  clay  muffle  (see  fig.  29),  and  electro- 
lysed it  by  means  of  a  current  from  six 
Smee's  elements,  and  two  flat  platinum  wire 
helices  as  electrodes,  during  thirty  minutes. 
The  conduction  was  free,  and  much  gas  was 
evolved  from  the  anode  only,  all  the  time.  The  anode  was 
not  corroded;  a  small  amount  of  lithium  was  deposited  upon 
the  platinum  cathode,  and  allo)  ed  with  it.  By  electrolysing 
a  larger  mass  of  the  salt  with  a  current  from  six  Grove's  cells 
and  a  thick  platinum  wire  cathode,  enclosed  within,  but  in- 
sulated from,  a  platinum  tube,  to  exclude  the  air  from  contact 
with  the  deposited  lithium,  the  action  was  copious  ;  with  a 
gold  anode,  the  gold  was  corroded  freely,  and  particles  of  it 
in  large  quantity,  floated  in  the  liquid  and  united  the  elec- 
trodes. The  cathode  swelled  greatly,  and  its  lower  end, 


Deposition  of  Sodium.  297 

bent  itself  towards  the  anode,  became  quite  grey  in  colour, 
and  split  in  the  direction  of  its  length. 

40.  Sodium. — Elec.-chem.  eqt.  =  23.  Nearly  all  the 
common  salts  of  sodium  are  freely  soluble  in  water,  and  may 
be  readily  obtained  in  a  pure  state,  by  neutralising  the  pure 
acids  with  pure  carbonate  of  sodium,  and  evaporating  the 
solutions.  The  fluoride  is  one  of  the  least  soluble. 

Soon  after  Sir  H.  Davy  first  isolated  sodium,  Gay-Lussac 
and  Thenard  showed,  that  iron  at  a  white  heat,  set  free  the 
metal  from  caustic  soda.  Other  investigators  soon  found 
that  carbon  acted  similarly.  I  have  also  observed  that 
crystals  of  silicon,  thrown  into  melted  fluoride  of  sodium, 
evolved  small  bubbles  of  vapour,  which  exploded  and  burned 
with  a  yellow  flame,  on  arriving  at  the  surface  of  the  liquid. 
In  a  second  experiment,  seven  grains  of  the  dry  fluoride  in 
powder,  and  one  grain  of  the  crystals,  were  mixed,  and  heated 
to  redness  ;  the  silicon  lost  '15  of  a  grain  in  weight. 

Electrolysis  of  salts  of  sodium. — Sir  H.  Davy  first  electro- 
deposited  sodium  in  the  year  1807,  by  moistening  its  hydrate 
with  water  in  a  platinum  capsule,  which  acted  as  the  anode, 
dipping  a  platinum  wire  cathode  in  the  salt,  and  using  a 
current  from  a  battery  composed  of  100  to  200  cells.  He  also 
deposited  it  more  easily  into  mercury,  in  a  similar  way  to  that 
already  described  under  magnesium  (see  p.  287),  and  thus 
obtained  an  amalgam  of  the  two  metals. 

According  to  Faraday,  fused  borax  is  decomposed  by 
electrolysis  into  oxygen  and  sodium,  and  the  latter  takes 
oxygen  from  the  boracic  acid  and  sets  free  boron  (see  p.  46). 
According  to  Burckhard,  '  Carbonate  of  sodium  in  a  fused 
state  is  a  good  conductor  ;  by  electrolysis  it  is  decomposed 
into  carbonic  acid  and  soda,  but  a  small  portion  of  carbon 
is  also  set  free.'  He  -also  states,  that  fused  pyrophosphate  of 
sodium,  electrolysed  with  platinum  electrodes,  yields  phos- 
phide of  platinum,  but  the  chief  result  is,  that  the  salt  splits 
up  into  oxygen,  phosphorus,  and  soda  (*  Chemical  News,' 
vol.  xxi.  p.  238).  In  the  electrolysis  of  melted  sulphate  of 


298  The  A  rt  of  Electro-Metallurgy. 

sodium  with  platinum  electrodes,  sodium  is  deposited,  and 
combines  with  the  cathode  (Brester,  '  Chemical  News,'  vol. 
xviii.  p.  145).  A  fused  mixture  of  the  chlorides  of  calcium 
and  of  sodium,  yields  a  deposit  of  the  latter  metal,  when 
electrolysed  in  a  certain  manner  (Matthiessen,  Watts,  '  Dic- 
tionary of  Chemistry,'  vol.  i.  p.  715). 

By  electrolysing  a  solution  of  common  salt,  Higgins  and 
Draper  observed,  that  chlorine  was  set  free  at  the  anode,  and 
hydrogen  gas  and  soda  at  the  cathode ;  but  if  the  cathode 
consisted  of  mercury,  sodium  amalgam  was  produced . 

Hisinger  and  Berzelius,  electrolysed  a  solution  of  com- 
mon salt,  with  silver  electrodes ;  gas  was  evolved  at  the 
cathode,  and  after  a  time  at  the  anode  also  ;  the  anode  be- 
came covered  with  argentic  chloride,  the  liquid  near  it  con- 
tained dissolved  chlorine,  and  the  solution  near  the  cathode 
contained  free  soda  ;  with  lead  electrodes,  the  negative  wire 
evolved  gas,  and  received  a  deposit  of  crystals  of  lead,  and 
the  anode  became  coated  with  plumbic  chloride. 

I  electrolysed  a  saturated  aqueous  solution  of  sodic 
fluoride,  by  a  current  from  six  Grove's  cells,  with  platinum 
electrodes  ;  gas  was  evolved  from  the  anode,  and  emitted 
an  odour  of  ozone  powerfully.  From  the  electrolysis  of  sul- 
phide of  sodium,  Buff  concluded,  that  the  sodium  travelled 
towards  the  cathode,  and  all  the  sulphur  to  the  anode, 
('  Chemical  News,'  vol.  xv.  p.  279).  A  solution  of  ordinary 
phosphate  of  sodium,  is  resolved  by  electrolysis,  into  soda  at 
the  cathode,  and  phosphoric  acid  at  the  anode. 

41.  Potassium. — Elec.-chem.  eqt.  =  39-1.  As  the  salts 
of  potassium,  like  those  of  sodium,  are  very  numerous,  and 
are  rarely  electrolysed  for  the  purpose  of  depositing  their 
metal,  I  need  only  remark,  that  most  of  them  may  be  prepared 
in  a  pure  state,  by  neutralising  the  respective  acids  by  pure 
potassic  carbonate  ;  and  that  nearly  the  whole  of  them  are 
freely  soluble  in  water ;  and  I  must  refer  the  reader  to  a 
work  on  chemistry  for  special  chemical  information  respecting 
them. 


Deposition  of  Potassium.  299 

Soon  after  Sir  H.  Davy  first  isolated  potassium  by  elec- 
trolysis, Gay-Lussac  and  Thenard  showed,  that  the  metal  was 
also  set  free  by  the  contact  of  iron  with  melted  potash  at  a 
white  heat.  Other  investigators  found  subsequently,  that 
carbon  acted  similarly.  According  to  H.  St. -Claire  Deville, 
even  silver  deposits  potassium,  when  immersed  in  fused 
potassic  iodide ;  it  also  renders  an  aqueous  solution  of  iodide 
of  potassium  alkaline,  and  forms  argentic  iodide,  by  a  simi- 
lar reaction  ('The  Chemist,'  New  Series,  vol.  iv.  p.  329). 

Electrolysis  of  salts  of  potassium. — Sir  H.  Davy  first 
deposited  this  metal  in  the  year  1807,  by  the  influence  of  an 
electric  current  upon  wet  hydrate  of  potash,  in  a  precisely 
similar  way  to  that  which  he  employed  for  depositing  sodium. 
Since  that  time  it  has  been  found,  that  even  a  feeble  electric 
current  from  two  or  three  cells  of  any  ordinary  battery, 
passed  through  a  solution  of  the  common  salts  of  potassium 
(not,  however,  including  the  nitrate,  or  chlorate  ?,  bromate  ?, 
or  iodate  ?)  into  a  cathode  of  mercury,  converts  that 
metal  more  or  less  into  an  amalgam  of  potassium  ;  and  if 
the  cathode  is  composed  of  a  metal  which  does  not  readily 
absorb  the  deposit,  the  latter  at  once  decomposes  the  water, 
setting  free  hydrogen,  and  forming  potash.  For  instance, 
according  to  Faire  and  Roche,  in  the  electrolysis  of  solu- 
tions of  alkaline  carbonates  or  bicarbonates,  the  molecule 
splits  up  in  such  a  way,  that  an  atom  of  potassium  or  sodium 
is  set  free  at  the  cathode  and  liberates  hydrogen  ('  Chemi- 
cal News,'  vol.  xxx.  p.  63;  'Journal  of  the  Chemical  Society,' 
vol.  xii.  p.  86 1).  Buff  also  electrolysed  potassic  sulphides, 
and  concluded  that  the  metal  travelled  towards  the  cathode, 
and  the  sulphur  towards  the  anode  ('Chemical  News/ 
vol.  xv.  p.  279). 

Faraday  found,  that  by  passing  an  electric  current  through 
melted  iodide  of  potassium,  iodine  was  set  free  at  the  anode, 
and  potassium  at  the  cathode.  Jaquin  observed,  that  fused 
sulphide  of  potassium  yields,  by  electrolysis,  potassium  at 
the  cathode.  Mathiessen  states,  that  a  fused  mixture  of  the 


3OO  The  Art  of  Electro-Metallurgy. 

chlorides  of  calcium,  potassium,  and  sodium,  yields  a  deposit 
of  potassium,  when  electrolysed  in  a  certain  manner  (Watts, 
'Dictionary  of  Chemistry,'  vol.  i.  p.  715).  According  to 
Brester,  in  the  electrolysis  of  melted  caustic  potash,  an  anode 
of  either  platinum,  silver,  or  copper,  dissolves  in  the  fused 
alkali,  and  the  respective  metals  are  deposited  upon  the 
cathode.  The  electrolysis  of  melted  chlorate  of  potassium, 
with  a  platinum  anode,  yields  potassium,  which  unites  with 
a  cathode  of  copper  or  platinum.  Chlorine  and  oxygen 
(having  an  odour  of  phosphorus),  are  set  free  at  the  anode, 
and  form  thick  white  vapours  by  contact  with  water  ('  Chem- 
ical News,'  vol.  xviii.  p.  145). 

The  following  experiments  of  mine,  now  first  published, 
bear  upon  the  simultaneous  liberation  of  potassium  and  fluo- 
rine, by  means  of  electro-deposition: — I  fused  130  grains  of 
pure  fluoride  of  potassium  in  a  platinum  crucible,  within  a 
partially  covered  clay  muffle  (see  fig.  29,  p.  296)  inserted  in  the 
hole  in  the  top  of  one  of  my  gas  furnaces,  and  electrolysed  it 
during  two  and  a  half  hours,  by  means  of  a  current  from  six 
Smee's  cells,  and  two  flat  helices  of  platinum  wire  as  elec- 
trodes. There  was  free  conduction,  and  much  gas  (of  an 
odour  like  that  of  hydrofluoric  acid),  evolved  from  the  anode, 
but  none  from  the  cathode,  and  no  signs  of  any  deposit. 
The  anode  was  not  corroded,  nor  altered  in  weight.  I  also 
electrolysed  some  of  the  same  salt  in  a  state  of  fusion,  by 
means  of  a  current  from  six  Grove's  cells,  with  a  thick 
platinum  wire  as  the  anode,  and  the  platinum  vessel  as  the 
cathode;  great  heat  was  evolved,  and  violent  electrolytic  action 
occurred;  nearly  white-hot  metallic  globules  also  accumulated, 
and  exploded  repeatedly.  The  end  of  the  anode  fused,  and 
particles  of  platinum  ramified  from  it  in  white-hot  threads, 
and  a  short  electric  arc  (about  one-tenth  of  an  inch  in 
length)  was  produced. 

I  also  perfected  and  used,  a  somewhat  elaborate  platinum 
apparatus,  by  means  of  which  the  gas  from  the  anode,  was 
prevented  from  coming  in  contact  with  the  cathode,  and 


Electrolysis  of  Potassic-Fhwride.  30 1 

might  be  collected  ;  the  electrodes  being  enclosed  within 
(but  isolated  from)  two  wide  platinum  tubes.  One  thousand 
grains  of  the  perfectly  pure  salt  was  electrolysed  in  this 
apparatus,  by  means  of  a  current  from  six  Grove's  cells.  The 
anode,  which  was  a  solid  rod  of  platinum,  was  rapidly  cor- 
roded, and  was  thus  cut  off  at  the  level  of  the  liquid,  and 
stopped  the  current  ;  the  corroded  surface  was  very  bright, 
as  if  fused.  Potassium  was  deposited  upon  the  cathode. 
Much  spongy  platinum  was  diffused  in  the  melted  salt; 
and  the  apparatus  was  a  little  corroded  at  the  surface 
of  the  liquid.  No  gas  was  evolved  at  the  anode.  The 
deposited  potassium  did  not  alloy  with  the  stout  rod  of 
platinum  used  as  the  cathode.  55  '35  grains  of  grey  metallic 
platinum  were  found  in  the  saline  mass.  A  salt  of  platinum 
appeared  to  have  been  formed  at  the  anode,  then  dissolved 
or  diffused  throughout  the  liquid,  and  decomposed  by  the 
heat,  and  thus  the  liberated  fluorine  did  not  escape  at  the 
anode,  but  was  evolved  in  the  mass  of  the  liquid  generally, 
and  came  into  contact  with  the  liberated  potassium. 

Having  ascertained  the  electrical  relations  of  palladium, 
gold,  platinum,  and  iridium  in  the  fused  fluoride,  palladium 
being  the  most  positive,  and  iridium  the  most  negative,  I 
repeated  the  experiments  with  an  anode  of  iridium,  and  a 
current  from  three  Grove's  cells.  Copious  clouds  descended 
at  once  from  the  anode,  and  made  the  liquid  opaque ;  there 
was  also  a  violent  action  at  the  anode,  it  became  black, 
and  a  little  gas  was  evolved  from  it,  accompanied  by  an  acid 
odour,  like  that  of  a  mixture  of  sulphurous  anhydride  and  hy- 
drofluoric acid.  Potassium  was  freely  liberated  at  the  cathode, 
and  produced  occasional  explosions.  With  a  current  from 
six  cells,  the  anode  dissolved  rapidly,  and  soon  lost  thirty- 
eight  grains.  I  then  put  a  pure  gold  anode,  and  employed 
two  cells.  Gas,  of  a  feebly  acid  odour,  was  freely  evolved  at 
the  anode ;  and  with  a  current  from  six  cells,  was  very  copious, 
and  smelt  much  like  sulphurous  anhydride.  The  gold  dis- 
solved much  less  rapidly  than  the  iridium.  With  a  palladium 


3Q2  The  A  rt  of  Electro-Metallurgy. 

anode,  and  a  current  from  six  cells,  the  anode  rapidly  dis- 
solved, potassium  was  deposited,  and  exploded  frequently ; 
and  an  odour  like  that  of  hydrofluoric  acid,  was  strong,  much 
gas  being  liberated.  33*3  grains  of  free  metal  was  found  in 
the  saline  mass.  The  platinum  cathode  was  not  corroded. 
The  platinum  anode  was  dissolved  as  if  melted ;  the  iridium 
one  was  black  ;  the  palladium  one  was  oxidised  of  various 
colours.  The  platinum  vessel  was  cut  into,  at  the  level  of 
the  surface  of  the  liquid,  evidently  not  by  the  fused  fluoride 
of  potassium,  but  by  some  substance,  set  free  at  the  anode 
by  electrolysis.  In  another  instance,  I  electrolysed  the 
pure  fused  fluoride  with  a  large  platinum  anode,  small 
platinum  cathode,  and  a  current  from  three  Grove's  cells, 
during  half  an  hour.  Much  gas,  having  an  odour  of  ozone 
and  hydrofluoric  acid,  was  evolved  from  the  anode ;  and 
the  latter  dissolved  rapidly,  and  lost  thirty-seven  and  a 
half  grains  in  weight.  The  gas  reddened  test-paper.  The 
platinum  containing  vessel  was  corroded  at  the  line  of  surface 
of  the  liquid,  and  lost  about  eleven  grains.  About  fifty-one 
grains  of  free  metallic  platinum,  in  loose  powder,  was  found 
in  the  saline  residue.  Each  of  these  experiments  shows 
that  a  very  corrosive  substance  was  liberated  at  the  anode. 

I  electrolysed  the  fused  salt  with  a  gas-carbon  anode,  and 
a  platinum  wire  flat  helix  as  cathode,  with  a  current  from  six 
Smee's  cells.  Free  conduction  occurred,  and  much  gas  was 
set  free  from  the  anode  only.  The  part  of  the  anode  in  the 
liquid  was  not  visibly  corroded. 

I  also  electrolysed  about  eight  ounces  of  pure  double 
fluoride  of  hydrogen  and  potassium  (KF,  HF)  in  a  fused  state, 
during  half  an  hour,  at  about  300°  Fahr.,  with  a  current  from 
ten  Smee's  cells,  and  electrodes  of  stout  sheet  platinum. 
There  was  copious  conduction,  and  abundance  of  hydrogen 
evolved  at  the  cathode,  but  no  gas  from  the  anode,  which  was 
rapidly  corroded  away,  with  a  rough  surface,  and  lost  9*37 
grains.  The  salt  became  less  fusible  by  loss  of  hydrofluoric 
acid,  which  escaped  freely  all  the  time.  The  saline  residue 


Electrolysis  of  Potassic- Fluoride.  303 

contained  a  small  amount  of  dissolved  platinum  salt,  and 
nearly  nine  grains  of  free  metallic  platinum.  In  a  second 
experiment,  lasting  half  an  hour,  the  salt  was  kept  only  just 
fused,  and  a  small  gold  anode  was  employed.  The  con- 
duction was  free,  and  much  gas  was  evolved  from  the  cathode, 
and  a  film  of  bright  yellow  gold  spread  over  the  surface  of  the 
salt,  and  connected  the  electrodes,  unless  the  liquid  was 
continually  stirred.  The  anode  rapidly  dissolved  (more 
quickly  than  that  of  platinum),  and  the  salt  of  gold  at  once 
decomposed,  and  set  free  finely  divided  gold  as  a  dull  red- 
brown  powder  at  the  anode.  No  gas  appeared  at  the  anode 
at  any  time  ;  that  from  the  cathode,  detonated  on  applying  a 
light.  There  was  loose  red-brown  powder  of  gold,  weighing 
i  -4  grains,  upon  the  cathode,  but  only  a  faint  gilding,  weigh- 
ing '05  grain.  The  anode  was  corroded,  dull  and  rough,  and 
it  lost  6 '80  grains.  The  saline  residue  contained  no  dissolved 
gold,  but  5-85  grains  of  red-brown  powder,  containing  5-30 
grains  of  gold.  In  a  third  similar  experiment,  by  using  a  large 
sheet  platinum  anode,  and  a  small  platinum  cathode,  and  a 
current  from  ten  Smee's  cells,  during  two  hours,  the  phe- 
nomena were  the  -same  as  in  previous  experiments.  The 
anode  lost  twenty-eight  grains ;  much  loose  platinum  col- 
lected on  the  cathode,  which  was  neither  corroded,  nor 
alloyed.  The  saline  residue  contained  a  trace  of  dissolved 
platinum  salt,  and  nearly  all  the  corroded  platinum  in  a 
metallic  state.  In  a  fourth  experiment  I  continued  the 
Action  during  three  and  a  half  hours  ;  the  results  were  as 
before.  The  loss  of  the  anode  was  3573  grains.  The 
saline  residue  contained  a  small  quantity  of  dissolved 
double  fluoride  of  platinum  and  potassium,  which,  after 
being  well  washed,  was  dried,  and  heated  to  redness ;  it 
then  shot  about  as  if  gas  was  evolved  from  it.  In  a  fifth 
similar  experiment,  lasting  four  and  a  half  hours,  at  the 
lowest  possible  fusion  temperature,  more  of  the  brown  pla- 
tinum salt  formed  at  the  anode,  and  dissolved  in  the  liquid. 
The  anode  lost  64-81  grains.  In  a  last  experiment  I  electro- 


304  The  A  rt  of  Electro-Metallurgy. 

lysed  a  gently  fused  mixture  of  900  grains  of  the  pure  double 
salt,  and  one  hundred  grains  of  pure  argentic  fluoride,  with 
a  large  anode  of  platinum,  and  a  large  cathode  of  silver. 
Conduction  was  complete  with  ten  Smee's  cells.  No  gas 
was  evolved  at  either  electrode.  The  surface  of  the  anode 
disintegrated  rapidly,  and  lost  49*84  grains  in  four  and  a  half 
hours'  action.  The  separated  platinum  dissolved  only  to  a 
small  extent  in  the  liquid,  and  subsided,  in  admixture  with 
the  silver,  to  the  bottom  of  the  vessel,  as  a  fine  black  powder, 
weighing  73*93  grains,  which  lost  less  than  two  percent,  when 
heated  to  redness.  Some  grey  silver  powder  was  deposited 
upon  the  cathode.  In  all  these  experiments  with  the  acid 
fluoride,  films  continually  formed  upon  the  surface  of  the 
liquid  ;  they  came  from  the  cathode,  and  were  more  abun- 
dant, the  deeper  the  cathode  was  immersed. 

According  to  Faraday,  an  aqueous  solution  of  nitrate  of 
potassium  conducts  electricity  very  well,  yielding  hydrogen 
gas  at  the  cathode  (it  also  gives  ammonia  at  the  cathode 
[Daniell]).  He  also  observed  that  an  aqueous  solution  of 
cyanide  of  potassium,  yielded  by  electrolysis,  hydrogen  and 
potash  at  the  cathode  ;  at  the  anode  no  oxygen  was  evolved, 
but  the  adjacent  liquid  became  brown;  that  solutions  of 
sulphocyanide,  and  ferrocyanide  of  potassium  behaved  simi- 
larly ;  also  that  fused  cyanide  behaved  like  its  aqueous  solu- 
tion. (Gmelin's  '  Handbook  of  Chemistry/  vol.  i.  p.  458.) 

I  electrolysed  a  nearly  saturated  aqueous  solution  of 
pure  fluoride  of  potassium,  by  means  of  a  current  from  six 
Grove's  cells,  with  large  platinum  electrodes  ;  conduction  was 
copious,  and  the  liquid  acquired  a  nearly  boiling  temperature. 
Much  gas  (having  an  odour  like  that  of  a  mixture  of  ozone 
and  chlorine)  was  evolved  at  the  anode.  A  saturated  solution 
of  the  same  salt,  electrolysed  by  a  current  from  ten  large 
Smee's  cells,  with  large  platinum  electrodes,  evolved  gas  at 
each  electrode  ;  that  from  the  anode  smelt  powerfully  of 
ozone,  and  re-inflamed  a  red-hot  splint.  Several  other  ex- 
periments, with  variations  in  the  sizes  of  the  electrodes, 


Deposition  of  Rubidium  and  Ccesium.         305 

were  made,  and  with  addition  of  hydrofluoric  acid ;  but  the 
results  were  similar. 

I  saturated  some  pure  dilute  hydrofluoric  acid  of  40  per 
cent,  at  60°  Fahr.,  with  pure  double  fluoride  of  hydrogen 
and  potassium,  and  electrolysed  the  solution  by  a  current 
from  ten  Smee's  cells,  a  gold  anode,  and  a  platinum  cathode, 
during  five  and  a  half  hours.  Gas  was  evolved  freely  from 
both  electrodes,  and  a  strong  odour  of  ozone  was  observed. 
The  anode  lost  173  grains;  and  the  cathode  acquired  first 
a  gilded  appearance,  and  then  a  black  coating,  and  the  liquid 
became  black  with  finely  divided  matter. 

.Bourgoin  electrolysed  a  concentrated  solution  of  neutral 
tartrate  of  potassium  ;  gas  was  evolved  from  each  electrode, 
and  alkali  set  free  at  the  cathode.  The  anode  became  coated 
with  acid  tartrate,  and  evolved  nitrogen,  oxygen,  carbonic 
oxide,  and  carbonic  anhydride.  The  effect  of  the  current 
upon  a  solution  of  the  neutral  tartrate,  mixed  with  free  alkali, 
was  very  different ;  oxygen,  acetic  acid,  carbonic  anhydride, 
carbonic  oxide,  hydride  of  ethylene,  and  acetylene,  were  set 
free  at  the  anode  ('  Chemical  News,'  vol.  xvii.  p.  33). 

'42.  Rubidium. — Electro-chem.  eqt.  =  85,  and  Caesium, 
electro-chem.  eqt.  =  133.  These  metals  have  also  been 
electro-deposited  into  a  cathode  of  mercury,  in  a  similar 
manner  to  potassium,  sodium,  and  other  highly  electro- 
positive elements. 

43.  Ammonium. — H4N.  Electro-chem.  eqt.  =  i8.  Nearly 
all  the  salts  of  ammonium  are  freely  soluble  in  water,  and 
may  be  made,  by  adding  aqueous  ammonia,  or  a  solution  of 
the  carbonate,  to  the  respective  acids,  and  evaporating  the 
solutions. 

Electrolysis  of  anhydrous  ammonia. — Anhydrous  ammonia, 
liquefied  by  pressure,  has  been  eleotrolysed  by  Bleekrode, 
with  a  current  from  eighty  Bunsen's  cells;  gas  was  evolved, 
and  the  liquid  became  of  an  intensely  blue  colour.  Pie  also 
operated  with  a  current  from  3,240  cells  of  the  chloride  of 
silver  battery  of  Mr.  W.  De  la  Rue ;  the  anode  became 

x 


306  The  A  rt  of  Electro-Metallurgy. 

black,  much  gas  was  evolved,  and  the  liquid  became  deep 
blue.  On  stopping  the  current,  the  liquid  became  colourless. 
By  dissolving  rubidium,  potassium,  sodium,  or  lithium  in 
such  a  liquid,  I  also  obtained  deep  blue  solutions  ('  Proceed- 
ings of  the  Royal  Society,'  No.  141,  1873  ;  also  vol.  xxv. 
P-  323)  j  probably,  therefore,  metallic  ammonium  was  set 
free  and  dissolved. 

Electrolysis  of  salts  of  ammonium. — Sir  H.  Davy  electro- 
lysed a  saturated  solution  of  salammoniac,  with  an  anode  of/ 
platinum  and  a  cathode  of  mercury ;  chlorine  was  evolved 
at  the  former,  and  the  mercury  became  alloyed  with  ammo- 
nium, and  swelled  to  a  very  large  bulk. 

Hisinger  and  Berzelius  found,  that  on  electrolysing  a 
solution  of  salammoniac  with  silver  electrodes,  hydrogen 
was  evolved  at  the  cathode,  and  oxygen  at  the  anode,  and 
the  latter  electrode  acquired  a  coating  of  argentic  chloride. 
They  also  electrolysed  a  mixture  of  aqueous  ammonia  and 
sulphate  of  ammonium.  Hydrogen  was  evolved  at  the 
cathode,  and  nitrogen,  mixed  with  some  oxygen,  at  the 
anode.  A  gold  anode,  dissolved  in  such  a  liquid,  became 
covered  with  brown  fulminate  of  gold,  and  the  cathode  was 
gilded  (Gmelin's  '  Handbook  of  Chemistry,'  vol.  i.  p.  458). 

According  to  Seebeck,  a  moistened  cup  of  carbonate  of 
ammonium,  filled  with  mercury  as  a  cathode,  yields  by  elec- 
trolysis, the  ammoniacal  amalgam.  Faraday  electrolysed 
fused  nitrate  of  ammonium  ;  hydrogen  gas,  mixed  with  a 
little  nitrogen,  was  deposited  at  the  cathode.  The  aqueous 
solution  of  that  salt,  similarly  treated,  yielded  the  same 
mixture  at  the  cathode,  and  oxygen  at  the  anode.  I  electro- 
lysed gently  fused  ammonium  fluoride,  by  means  of  a  current 
from  six  Grove's  cells,  a  thick  platinum  wire  anode,  and  a 
large  platinum  sheet  cathode.  The  conduction  was  copious, 
and  heat  was  evolved.  Much  gas  was  liberated  at  the  anode, 
but  no  odour  of  ozone. 

Dry  nitrate  of  ammonium  condenses  gaseous  ammonia, 
and  becomes  a  liquid ;  the  solution  is  a  good  electrolyte,  and 


Deposition  of  Metalloids.  307 

yields  ammonia  and  hydrogen  at  the  anode.  Anodes  of 
silver,  copper,  lead,  zinc,  and  magnesium,  dissolve  in  it,  but 
one  of  mercury  becomes  coated  with  an  insoluble  compound. 
When  the  anode  is  corroded,  no  nitrogen  is  liberated  from  it 
(Divers,  '  Chemical  News/  vol.  xxvii.  p.  37  ;  '  Proceedings 
of  the  Royal  Society,'  vol.  xxi.  p.  109). 

According  to  A.  Favre,  under  the  influence  of  the  cur- 
rent, ammonic-oxide  is  decomposed  thus: — ist.  3(NH4)2 
O  =  3(NH4)2  +  O3.  The  three  equivalents  of  ammonium 
set  at  liberty,  decompose  the  water  like  potassium  or  sodium, 
thus:— 2nd.  3(NH4)2  +  3H2O  =  3(NH4)2O  +  3H2.  The 
oxygen  of  equation  No.  i,  reacting  upon  the  ammonium, 
gives: — 3rd.  O  +  NH4  =  N  +  2H2O.  The  first  equation 
represents  the  electrolysis  proper  ('  Journal  of  the  Chemical 
Society,'  vol.  ix.  p.  985). 


CLASS  VII.     DEPOSITION    OF    METALLOIDS. 

TITANIUM  —  SILICON  —  BORON  —  CARBON  —  PHOSPHORUS  — 
SELENIUM — SULPHUR — IODINE  — BROMINE — CHLORINE  — 
FLUORINE— OXYGEN — NITROGEN. 

Although  this  book  is  one  on  the  electro-deposition  of 
metals,  it  can  hardly  be  considered  complete,  unless  some- 
thing is  said  about  the  deposition  of  the  metalloids  or  non- 
metallic  elementary  substances,  because  the  two  classes  of 
bodies  are  so  closely  related  to  each  other  in  the  electrolysis 
of  their  compounds. 

44.    Deposition  of  titanium. — Elec.-chem.    eqt.  =  $2 

4 

=  12*5.  This  element  does  not  appear  to  have  been  yet 
electro-deposited.  Titanic  acid  is  the  most  usual  com- 
pound of  it  obtainable  in  a  state  of  purity ;  it  dissolved 
very  slowly  in  pure  dilute  hydrofluoric  acid,  and  by  evapo- 
rating the  solution  to  dryness,  a  white  and  somewhat  deli- 
quescent salt  remained.  I  found  that  a  heap  of  crystals  of 

X2 


308  The  Art  of  Electro-Metallurgy. 

nitro-cyanide  of  titanium,  conducted  freely,  an  electric  current 
from  sixty  Smee's  elements,  and  that  a  single  crystal  pressed 
between  the  terminal  wires,  became  red-hot,  and  then  ex- 
hibited a  splendid  white  light. 

45.  Silicon. — Elec.-chem.  eqt.=  —  =7*0.     In  some  ex- 

4 

periments  with  silicon  (which  I  had  fused  into  lumps)  I  found 
that  the  pieces  conducted  sparingly,  a  current  from  twelve 
Smee's  elements;  and  that  in  dilute  sulphuric  acid,  the 
silicon  was  strongly,  but  only  temporarily,  electro-positive  to 
platinum.  Silicon  is  generally  strongly  electro-positive  to 
other  substances  in  fused  fluorides,  and  like  carbon,  is  much 
more  electro-positive  at  very  high  temperatures  ;  at  such 
temperatures,  it  sets  free  sodium  from  its  fluoride  (see  p.  297). 
Some  of  the  electrical  relations  of  silicon  have  already  been 
given  (see  pp.  66,  67).  Phipson  states  that  magnesium 
separates  silicon  from  silica  at  a  high  temperature  ('  Proceed- 
ings of  Royal  Society,'  vol.  xiii.  p.  217;  'Chemical  News,' 
vol.  ix.  p.  219). 

According  to  Becquerel,  crystals  of  silicon  may  be  de- 
posited upon  a  platinum  cathode,  in  a  saturated  solution  of 
gelatinous  silica  in  hydrochloric  acid  ('  Chemical  News,'  vol. 
xii.  p.  4).  According  to  Golding  Bird,  silicon  may  also  be 
deposited  from  a  solution  of  its  fluoride  in  alcohol  ('  Philo- 
sophical Transactions  of  the  Royal  Society,'  1837,  p.  37  ; 
Golding  Bird's  '  Natural  Philosophy,'  5th  edition,  p.  408). 
I  electrolysed  fused  pure  silico-fluo'ide  of  potassium  in  a 
platinum  vessel,  with  platinum  electrodes;  silicon  was  de- 
posited upon  the  cathode,  and  formed  a  fusible  alloy  with  it. 

46.  Boron. — Elec.-chem.    eqt.  =  —-=  10-33.     Phipson 

states,  that  magnesium  in  contact  with  boracic  acid  in  a  fused 
state,  liberates  boron  ('  Proceedings  of  the  Royal  Society,' 
1864,  vol.  xiii.  p.  217;  '  Chemical  News,'  vol.  ix.  p.  219). 

.   *  Boron   was  first  electro-chemically  isolated  by  Davy. 
He  states  that  when  boracic  acid  is  exposed  between  two 


Deposition  of  Silicon,  Boron,  and  Carbon.      309 

surfaces  of  platinum,  receiving  at  the  same  time  all  the  action 
of  a  current  from  300  cells,  an  olive-brown  matter  is  formed 
upon  the  negative  surface,  gradually  increasing  in  thickness, 
and  finally  becoming  black.  The  isolated  body  is  boron.' 
('  Chemical  News,'  vol.  xii.  p.  3.)  Fused  borax  yields  oxygen 
gas  at  the  anode,  and  boron  at  the  cathode.  The  boron  is 
separated  by  indirect  action ;  the  current  resolves  the  soda 
into  oxygen  and  sodium,  and  the  latter  separates  boron 
from  the  boracic  acid  (Faraday,  Gmelin's  '  Handbook  of 
Chemistry,'  vol.  i.  p.  460).  According  to  Burckhard,  pure 
boracic  acid  in  a  state  of  fusion  is  a  non-conductor,  but  fused 
borax  conducts,  suffers  electrolysis,  and  a  series  of  com- 
pounds are  formed  or  volatilised ;  but  the  chief  result  is. 
that  the  salt  is  resolved  into  oxygen  at  the  anode,  and  soda 
and  boron  at  the  cathode  ('  Chemical  News,'  vol.  xx  . 
p.  238).  I  have  found  that  by  the  electrolysis  of  pure  boro- 
fluoride  of  potassium  in  a  fused  state,  with  platinum  elec- 
trodes, the  cathode  became  rough  and  brittle,  by  being 
converted  into  a  compound  with  electro-deposited  boron. 


47.  Carbon. — Elec.-chem.  eqt.  =  —  =3*0.     According 

4 

to  Phipson,  magnesium  in  contact  with  carbonate  of  sodium 
at  a  high  temperature,  sets  free  carbon  abundantly  ('Proceed- 
ings of  the  Royal  Society,'  1864,  vol.  xiii.  p.  217;  'Chemi- 
cal News,'  vol.  ix.  p.  219).  Deville  states,  that  metallic 
aluminium  deposits  carbon,  from  carbonate  of  potassium  in 
a  state  of  fusion  ('Chemist,'  New  Series,  vol.  iv.  p.  481). 

I  have  electro-deposited  perfectly  pure  carbon,  from  the 
pure  carbonates  of  potassium  and  sodium  in  a  state  of  fusion, 
adding  in  some  cases  a  little  silicate  of  potassium,  or  fluoride 
of  silicon  and  potassium  ;  the  deposit  was  black,  non-crystal- 
line, insoluble  in  all  acids,  burned  with  a  glow,  and  left  no 
residue.  According  to  P.  Burckhard,  fused  carbonate  of 
sodium  is  a  good  conductor,  and  yields  by  electrolysis, 
carbonic  anhydride,  soda,  and  a  small  portion  of  carbon 
('  Chemical  News,'  vol.  xxi.  p.  238).  Researches  on  the 


3  1  o  The  Art  of  Electro-  Metallurgy. 

electro-deposition  of  carbon  are  interesting,  with  reference 
to  the  possibility  of  the  artificial  formation  of  diamonds. 

I  have  found  that  carbonic  anhydride,  liquefied  by  pres- 
sure, does  not  conduct  a  current  from  forty  Smee's  elements,- 
and  is  a  powerful  insulator  of  electricity  (*  Transactions  of 
the  Royal  Society,'  i86r,  p.  85).  According  to  Bleekrode 
and  W.  De  la  Rue,  neither  liquefied  cyanogen  (C2N2),  liquid 
carbonic  anhydride  (CO2),  carbonic  bisulphide  (CS.2),  nor 
benzine  (C6H6),  were  decomposed  by  a  current  from  5,640 
cells  of  a  chloride  of  silver  battery  (*  Proceedings  of  the 
Royal  Society/  vol.  xxv.  pp.  324-326). 

48.  Phosphorus.—  Elec.-chem.  eqt.=  ^1=  10-33. 


electric  current  resolves  a  solution  of  ordinary  phosphate  of 
sodium,  into  soda  at  the  cathode,  and  phosphoric  acid  at 
the  anode.  The  electrolysis  of  concentrated  phosphoric 
acid,  produces  a  metallic  phosphide  upon  a  cathode  of  copper 
or  platinum  (H.  Davy).  Acid  phosphate  of  sodium  in  a 
state  of  fusion,  yields  hydrogen  at  the  cathode  (Faraday, 
Gmelin's  '  Handbook  of  Chemistry,'  vol.  i.  p.  460).  Accord- 
ing  to  Burckhard,  fused  pyrophosphate  of  sodium,  yields  by 
electrolysis,  phosphorus,  oxygen,  and  soda;  and,  with  a 
platinum  anode,  phosphide  of  platinum  is  formed  ('  Chemical 
News,'  vol.  xxi.  p.  238). 

49.  Selenium.  —  Elec.-chem.    eqt.   =   &$    =     3975- 

During  the  electrolysis  of  an  aqueous  solution  of  selenate  of 
nickel,  containing  selenate  of  sodium,  and  free  selenic  acid, 
I  have  repeatedly  observed  an  abundant  deposit  of  bright 
red  selenium  upon  a  platinum  cathode  ;  the  deposition  of 
selenium  ceased  on  neutralising  the  acid  with  ammonia. 

50.  Sulphur.  —  Elec.-chem.  eqt.  =  ^  =  16.     A  yellow 

solution  of  sulphide  of  potassium,  yields  a  quantity  of  sul- 
phur at  the  anode,  and  hydrogen  gas  at  the  cathode  ;  fused 
sulphide  of  silver  is  also  slightly  decomposed  by  electro- 


Deposition  of  Iodine,  Bromine,  and  Chlorine.    3 1 1 

lysis,  into  sulphur  at  the  anode,  and  silver  at  the  cathode 
(Faraday,  '  Gmelin's  Handbook  of  Chemistry,'  vol.  i.  p.  456)- 
An  aqueous  solution  of  sulphurous  anhydride,  yields  sulphur 
and  hydrogen  at  the  cathode  (De  la  Rive). 

51.  Iodine. — Elec.-chem.  eqt.  =  127.      Liquefied    an- 
hydrous hydriodic  acid  (HI),  does  not  conduct  the  current 
from  eighty  Bunsen's  cells  (Bleekrode,  '.Proceedings  of  the 
Royal  Society,'  vol.  xxv.  p.  323).      An  aqueous  solution  of 
iodic  acid,  yields  by  electrolysis,  oxygen  at  the  anode,  and 
iodine  alone  at  the  cathode.      Concentrated  hydriodic  acid, 
yields  iodine  alone  at  the  anode ;  but  the  dilute  acid  gives 
iodine  and  oxygen.     According  to  Faraday,  fused  iodide  of 
potassium,  or  iodide  of  lead,  yields  iodine  at  the  anode. 

52.  Bromine. — Elec.-chem.  eqt.=  80.  Anhydrous  hydro- 
bromic  acid  (HBr),  in  the  liquid  state,  does  not  conduct  the 
current  from  eighty  Bunsen's  cells  (Bleekrode,  *  Proceedings 
of  the  Royal  Society/  vol.   xxv.  p.  323).     Aqueous  hydro- 
bromic  acid,  deposits  by  electrolysis,  bromine  at  the  anode, 
and  hydrogen  at  the  cathode. 

53.  Chlorine. — Elec.-chem.  eqt.  =  35-5.     Liquefied  an- 
hydrous  hydrochloric  acid   (HC1),  does  not  conduct   the 
current,  even  from  as  many  as  5,640  cells  of  a  chloride  of 
silver  battery  (Bleekrode  and  W.  De  la  Rue,  '  Proceedings 
of  the  Royal  Society,'  vol.  xxv.  p.  325).  Concentrated  hydro- 
chloric acid  gives  hydrogen  at  the   cathode,  and  chlorine 
alone  at  the  anode  ;   and  only  after   considerable  dilution 
with  water,  does  oxygen  begin  to  be  deposited  along  with 
the  chlorine.     An  aqueous  solution  of  salammoniac  yields 
chlorine  at  the  anode,  and  hydrogen  and  ammonia  at  the 
cathode;  and  one   of  common  salt,  gives  chlorine  at  the 
anode,  and  hydrogen  and  soda  at  the  cathode.     According 
to  Faraday,  fused  chloride  of  lead,  and  chloride  of  silver, 
yield  chlorine  at  the  anode,  and  the  metal  at  the  cathode. 

54.  Fluorine. — Elec.-chem.  eqt.  =  19-0.     I  have  repeat- 
edly observed,  that  aqueous  solutions  of  metallic  fluorides, 
yield  oxygen  at  the  anode,  because  water  is  decomposed 


3  r  2  The  A  rt  of  Electro-Metallurgy. 

more  readily  than  fluorides;  but  with  certain  fluorides  in  a 
state  of  fusion,  a  highly  corrosive  substance  is  evidently 
liberated.  (See  the  electrolysis  of  various  fused  fluorides, 
already  described,  especially  that  of  fluoride  of  potassium, 
pp.  121,  300-303.)  By  the  electrolysis  of  pure  anhydrous  hy- 
drofluoric acid  (see  p.  96),  I  found  that  the  acid  conducted 
readily  a  current  from  ten  Smee's  cells,  but  evolved  no 
fluorine  from  an  anode  either  of  palladium  (see  p.  115), 
platinum  (see  p.  120),  or  gold  (see  p.  126),  and  anodes  of 
the  densest  varieties  of  carbon  were  instantly  disintegrated. 
And  by  electrolysis  of  the  pure  aqueous  acid,  with  elec- 
trodes of  platinum,  ozone  and  ordinary  oxygen  were  alone 
evolved  at  the  anode  ('Phil.  Trans.  Roy.  Society/  1869, 
P-  173). 

55.  Oxygen. — Elec.-chem.  eqt.  =  L_  =8.   Water,  to  which 

/  2 

almost  any  acid  or  salt  has  been  added  (in  not  too  great 
quantity),  in  order  to  make  it  conduct,  yields  by  electrolysis, 
oxygen  at  an  anode  of  platinum. 

56.  Nitrogen.—  Elec.-chem.  eqt.  =  H       4-66.     A  con- 
centrated aqueous  solution  of  ammonia,  with  electrodes  of 
iron,  yields  hydrogen  at  the  cathode,  and  pure  nitrogen  at 
the  anode  (Hisinger  and  Berzelius). 


313 


SPECIAL  TECHNICAL  SECTION. 


SECTION    B. 

HAVING  described  all  the  methods  in  practical  use  for 
depositing  metals,  and  as  briefly  as  I  have  been  able,  the 
circumstances  under  which  almost  every  known  metal  has 
been  deposited,  so  that,  any  one  wishing  to  apply  to  practical 
uses,  the  deposition  of  metals  not  yet  so  employed,  may  be 
able  to  make  a  successful  commencement,  I  will  now  give 
a  number  of  special  technical  points  of  information,  necessary 
for  the  successful  prosecution  oi  the  art,  which  could  not 
be  so  conveniently  described  in  the  preceding  sections  of 
the  book. 

FIG.  30. 


General    workshop  arrangements. — Before  commencing, 
on  a  practical  scale,  the  art  of  electro-metallurgy,  it  will  be 


3 1 4  The  A  rt  of  Electro-Metallurgy. 

necessary  to  provide  a  depositing-room,  vats  for  solutions, 
scouring  and  cleaning  apparatus,  batteries,  a  magneto-electric 
machine,  or  other  source  of  electric  power ;  the  various 
chemicals  necessary  for  making  and  reviving  depositing 
liquids  acids  for  cleaning  and  '  stripping ' ;  materials  for 
making  moulds,  and  preparing  their  surfaces,  &c.,  &c. 

The  establishment  should  consist  of  several  rooms,  and 
an  open  yard  ;  i.e.,  a  room  for  depositing  copper,  another 
for  silver,  and  a  smaller  and  more  private  one  leading  out  of 
it,  for  gilding.  The  rooms  should  be  upon  the  ground-floor, 
on  account  of  the  weight  of  the  vats  containing  the  solutions, 
and  should  be  provided  with  a  cemented  floor,  and  a  drain 
running  into  a  small  cemented  well,  to  recover  valuable 
liquids  which  may  be  accidentally  spilled.  They  should 
be  well  lighted  and  ventilated,  because  of  the  noxious  vapours 
sometimes  evolved  ;  and  should  contain  conveniences  for 
the  placing  of  the  vats,  washing- troughs,  and  scratch-brush 
lathes  ;  and  be  provided  with  a  plentiful  supply  of  water. 
An  outhouse  for  containing  a  large  iron-boiler ;  also  a 
covered  shed  in  a  yard  (for  the  processes  of  dipping),  will 
be  necessary.  The  yard  is  required  for  precipitating  solu- 
tions, from  which  the  poisonous  vapour  of  prussic  acid  is 
evolved.  Instead  of  an  outhouse,  a  separate,  but  adjoining 
room,  may  be  used,  in  which  to  erect  the  iron  boiler,  for  con- 
taining caustic  potash  solution,  for  cleaning  greasy  and  other 
articles.  If  voltaic  batteries  are  much  employed,  they  are 
best  placed  outside  the  plating-room,  because  the  vapour 
arising  from  them  is  unhealthy,  and  also  tarnishes  the 
articles.  If  a  magneto- electric  machine  is  used,  it  is  also 
best  to  have  it,  and  the  engine  which  drives  it,  at  a  distance 
from  the  cleaning  liquids,  or  in  an  adjoining  dry  apartment. 

Accessible  from  each  of  the  rooms,  should  be  erected  a 
low  furnace,  having  a  long  horizontal  flue  covered  with 
plates  of  iron,  upon  which  are  placed  several  large  iron  trays 
filled  with  hot  sawdust,  in  which  the  wet  articles  are  to  be 
dried.  Each  depositing-room  should  be  supplied  with  a 


Vats  for  Solutions.  315 

water-tap,  and  several  large  wooden  tubs  or  troughs  filled 
with  water,  for  washing  the  articles.  The  *  pickling '  and 
'stripping'  liquids  are  best  kept  in  large  stoneware  pans, 
under  the  open  roof  in  the  yard.  In  the  gilding-room,  will 
be  placed  iron  vessels  for  containing  the  gilding  liquids;  these 
vessels  are  usually  of  enamelled  iron,  either  wrought  or  cast, 
and  should  be  supported  on  iron  frames,  with  large  Bunsen 
burners  beneath,  for  the  purpose  of  heating  the  liquids  ;  flues 
should  also  be  provided  to  convey  the  products  of  combus- 
tion trom  the  burners  into  the  open  air.  Accessible  also  to 
each  of  the  rooms,  should  be  placed  several  scratch -brush 
lathes,  for  scouring  and  brightening  the  articles.  Round  the 
walls  of  the  coppering  and  silvering  rooms,  should  be  fixed 
well-insulated  stout  copper  wires,  to  convey  the  electric 
currents  from  the  batteries  or  magnetic  machines  to  the  vats. 
For  the  gilding-room  these  will  not  be  required,  because 
gilding  is  usually  effected,  by  means  of  a  small  voltaic  battery, 
or  thermo-electric  pile,  placed  close  at  hand. 

Vats  for  solutions. — The  construction  of  the  vats  for 
containing  silver  solutions,  has  been  already  described  (see 
p.  169) ;  those  for  containing  sulphate  of  copper  solution,  are 
usually  made  of  wood,  lined  with  a  thick  sheet  of  gutta- 
percha,  so  that  the  liquid  shall  not  come  into  contact  with 
the  wood.  According  to  Berthoud,  a  good  mixture  for  lining 
vats  to  contain  sulphate  of  copper  solution,  is  composed  of 
six  parts  of  Burgundy- pitch,  and  one  of  gutta-percha,  cut 
into  very  small  pieces  ;  the  whole  being  thoroughly  mixed 
by  melting  and  kneading.  The  silver-plating  vats  are  some- 
times placed  in  the  middle  of  the  room,  but  more  frequently 
against  a  wall  where  the  sunlight  does  not  fall  directly  upon 
the  solutions. 

Cleaning  articles  for  receiving  a  deposit. — All  articles  which 
are  to  receive  a  deposit,  require  to  be  made  scrupulously 
clean,  especially  if  it  is  wished  to  make  the  coating  adhere 
firmly  to  the  receiving  surface.  It  is  the  practice  before 
plating  an  article,  to  make  its  sur  ace  not  only  perfectly 


3 1 6  The  A  rt  of  Electro-Metallurgy. 

clean,  but  also  smooth,  by  means  of  the  revolving  '  scratch- 
brush,'  and  by  other  methods.  Articles  of  copper  are 
usually,  not  '  scratch-brushed,'  but  dipped. 

The  processes  of  cleansing,  are  both  of  a  mechanical  and 
chemical  nature.  The  mechanical  means,  are  the  usual  ones 
of  filing,  scrubbing,  and  scouring,  with  various  gritty  materials. 
Emery-cloth  is  employed  when  the  articles  are  dry,  and  fine 
silver- sand  and  a  hand-brush,  or  piece  of  canvas,  when  they 
are  wet.  In  addition  to  this,  an  instrument  called  a  '  scratch- 
brush  '  is  continually  used,  and  cannot  be  dispensed  with. 

A  '  scratch-brush '  is  merely  a  bundle  of  fine  and  hard 
brass  wires,  about  six  or  eight  inches  long,  bom  id  round  very 
tightly  with  other  wire,  except  at  the  ends  (see  fig.  31). 


These  wires  are  of  various  degrees  of  fineness,  and  are 
also  annealed  to  different  degrees,  to  suit  the  various  kinds  of 
work.  Four  of  such  brushes  are  usually  fixed  in  grooves 
upon  the  outside  of  the  chuck  of  a  lathe,  so  that  the  wires 
are  parallel  with  the  axis  of  the  chuck  (see  fig.  32).  Another 
form  of  scratch-brush,  in  which  the  wires  are  radial  instead  of 
parallel  is  shown  in  fig.  33. 


FIG 


To  use  these  brushes,  a  lathe  is  required.  A  ;  scratch- 
brush  lathe,'  suitable  for  cleaning  small  articles,  is  represented 
in  the  annexed  figures  33  and  34. 

Above  the  revolving  brush,  is  placed  a  cistern  containing 
stale  beer,  a  little  of  which  is  allowed  to  dribble  upon  the 


Cleaning  Articles  to  receive  a  Deposit.         317 

articles  during  the  process  of  brushing,  and  the  brushes  are 
surrounded  by  a  screen,  to  prevent  splashing. 

The  chemical  methods  of  cleaning,  consist  in  immersing 
the  articles  for  a  greater  or  less  period  of  time,  in  various 
acids  or  alkalies,  according  to  the  nature  of  the  metals. 
Alkalies  are  usually  employed  hot,  and  are  generally  used 
for  removing  greasy,  tarry,  or  resinous  matters ;  and  acids 

FIG.  33- 


are  generally  used  cold,  after  the  greasy  matters  have  been 
removed.  The  alkalies  are  kept  in  iron  vessels,  and  the 
acids  in  stoneware  pans,  &c. 

The  alkali  commonly  employed  is  caustic  potash,  because 
it  is  the  strongest.  A  solution  of  it  is  prepared,  by  adding 
freshly-made  cream  of  lime,  to  a  boiling  solution,  composed 
of  about  half  a  pound  or  a  pound  of  pearlash,  to  each  gallon 


The  Art  of  Electro-Metallurgy. 


of  water,  contained  in  an  iron  boiler,  until  a  small  quantity  of 
the  clear  liquid  gives  no  effervescence,  on  adding  to  it  a  few 
drops  of  dilute  hydrochloric  acid.  The  precipitate  formed 
in  the  mixture,  is  carbonate  of  lime,  and  may  be  thrown 
away.  As  this  liquid  rapidly  absorbs  carbonic  acid  from 
the  air,  it  should  be  kept  covered  as  much  as  possible ;  and 
a  small  quantity  of  the  cream  of  lime,  should  be  added  to 
it  occasionally,  to  renew  its  full  degree  of  causticity.  The 

FIG.  34. 


articles  to  be  cleaned,  are  immersed  for  a  short  time  in  the 
boiling  hot  liquid  ;  copper  only  requires  to  be  immersed  a 
few  seconds.  Copper  articles,  joined  by  solder  containing 
tin,  must  not  remain  long  in  the  liquid,  or  the  tin  will  dissolve, 
and  be  deposited  upon  the  adjoining  parts  of  the  copper, 
and  blacken  them. 

Several  kinds  of  acid  liquids  are  employed,  viz.,  dilute 


Cleaning  Articles  to  receive  a  Deposit.         319 

sulphuric,  strong  nitric,  and  various  mixtures  of  them.  Nitric 
acid  for  dipping,  contains  about  10  percent,  of  sulphuric 
acid,  and  has  a  sp.  gr.  of  about  1*52. 

The  special  methods  of  cleaning,  depend  both  upon  the 
nature  of  the  impurities  upon  the  surface,  and  of  the  metal 
beneath.  All  greasy  articles,  of  whatever  metal  they  are 
composed,  are  always  dipped  into  the  potash  solution,  and 
then  usually  thoroughly  swilled  in  water.  Articles  composed 
of  lead,  tin,  Britannia  metal,  or  pewter,  are  dipped  in  the 
caustic  potash,  and,  with  or  without  swilling,  transferred  at 
once  to  the  depositing  solution.  Those  of  zinc  are  some- 
times treated  similarly  ;  and  at  other  times,  are,  after  swill- 
ing, dipped  in  dilute  sulphuric  acid,  washed  again,  and  trans- 
ferred to  the  plating  liquid.  For  cleaning  iron  articles,  a 
cold  mixture  of  about  twenty  measures  of  water,  and  one 
of  sulphuric  acid,  is  frequently  used ;  but  a  better  liquid 
is  composed  of  one  gallon  of  water,  and  one  pound  of  sul- 
phuric acid,  with  one  or  two  ounces  of  zinc  dissolved  in 
it ;  to  this  is  added  half  a  pound  of  nitric  acid.  This 
mixture  leaves  the  iron  quite  bright,  whereas  dilute  sul- 
phuric acid  alone,  leaves  it  black,  or  of  a  different  appear- 
ance at  the  edges.  For  glassy  patches  upon  cast  iron, 
(which  usually  consist  of  silicate  of  iron),  hydrofluoric  acid  is 
used ;  it  is  kept  in  a  bottle  of  gutta-percha  closed  by  a 
bung  of  indiarubber  ;  it  must  not  be  allowed  to  come  into 
contact  with  glass  vessels,  nor  must  the  mouth  of  the  bottle 
be  left  open.  The  fumes  from  it  are  extremely  dangerous 
to  inhale.  Articles  of  iron  which  have  been  cleaned  in 
acids,  and  the  adhering  acid  washed  away  with  water,  may 
be  protected  from  rusting,  by  continued  -immersion  in 
lime-water,  a  solution  of  washing-soda,  or  in  water  contain- 
ing any  caustic  alkali,  until  required. 

Articles  of  pure  silver,  are  best  dipped  in  a  heated  state, 
in  dilute  boiling  sulphuric  acid,  after  having  been  immersed 
in  the  alkali  and  swilled  ;  or  they  may  be  dipped  cold,  in 
strong  and  pure  nitric  acid,  and  then  in  distilled  water.  New 


320  The  A  rt  of  Electro-Metallurgy. 

anodes  of  rolled  silver  are  often  greasy,  and  have  a  film  of 
oxide  of  iron  upon  them  ;  they  should  be  scoured  with  caustic 
alkali,  or  be  heated  to  redness,  before  placing  them  in  the 
plating  solution 

For  articles  of  copper,  brass,  or  German  silver,  a  series  of 
liquids  is  used  ; — first,  strong  nitric  acid;  second,  'dipping 
liquid '  (consisting  of  sixty-four  parts  of  water,  sixty-four  of 
sulphuric  acid,  thirty-two  of  nitric  acid,  and  one  of  hydro- 
chloric acid)  ;  and,  third,  'spent'  liquid,  i.e.,  either  nitric 
acid  or  dipping  liquid,  which  has  become  weak.  Such 
articles  are  often  partly  cleaned,  by  heating  them  to  dull 
redness,  and  then  plunging  them  into  dilute  sulphuric  acid. 
(Those  having  solder  upon  them  are  not  heated  thus  ; 
articles  of  cast  bronze  are  also  not  heated  in  this  way,  be- 
cause they  would  be  liable  to  crack.)  They  are  then  soaked 
in  old  aqua-fortis,  until,  after  rinsing,  they  look  uniformly 
metallic  ;  they  may  then  be  dipped  in  strong  aqua-fortis  for 
a  few  seconds,  and  swilled.  The  straw-coloured  aqua-fortis 
acts  the  best :  the  white  acts  too  feebly,  and  the  red  too 
strongly.  It  is  necessary  to  have  a  large  bulk  of  the  acid,  in 
order  that  it  may  not  be  come  too  warm  by  the  action. 

To  dip  gilding  metal  bright. — Immerse  it  in  weak  aqua- 
fortis until  there  is  a  black  scale  formed;  then  dip  it  in  '  strong 
pickle'  for  a  few  minutes.  (N.B.  'strong pickle'  is  exhausted 
aqua-fortis  ;  '  weak  pickle '  is  the  same  diluted  with  the  wash- 
ings.) Then  dip  it  quickly  into  strong  aqua-fortis,  and  then 
into  several  waters  in  succession.  There  are  various  mix- 
tures, which  may  be  employed  for  imparting  a  bright  lustre 
by  dipping  ;  the  following  is  one  of  them  :  one  measure  of 
nearly  exhausted  aqua-fortis,  two  of  water,  and  six  of  hydro- 
chloric acid  ;  the  articles  of  copper,  brass,  or  German  silver 
should  be  immersed  in  it  a  few  minutes,  or  until,  after  wash- 
ing off  the  black  mud  which  entirely  covers  them,  they  look 
bright ;  they  are  then  cleaned  and  dipped  again.  To  obtain 
a  dead  lustre,  the  articles  of  copper  or  its  alloys,  are  dipped 
into  a  cold  mixture  of  one  volume  of  oil  of  vitriol  mixed 


Cleaning  Articles  to  receive  a  Deposit.         321 


with  two  volumes  of  yellow  aqua-fortis,  and  a  little  common 
salt  then  added  ;  the  articles  must  remain  some  time  in  the 
bath,  and  then  be  quickly  dipped  into  the  liquid  for  pro- 
ducing a  bright  lustre,  and  immediately  rinsed.  Articles 
composed  of  German  silver,  are  more  difficult  to  impart  a 
proper  appearance  to,  by  the  process  of  dipping,  than  those 
of  copper  or  brass. 

Old  aqua-fortis  is  revived  to  a  certain  extent,  by  addition 
of  oil  of  vitriol  and  common  salt;  the  sulphuric  acid  decom- 
poses the  nitrate  of  copper  in  it,  and  also  the  common  salt, 
and  sets  free  nitric  and  hydrochloric  acids  ;  and  crystals  of 
sulphate  of  copper  form  at  the  bottom  of  the  liquid.  All  the 
nitric  acid  may  be  utilised  in  this  manner. 

FIG.  35- 


FIG.  36. 


Small  articles  are  either  strung  upon  wires  (see  fig.  35) 
of  the  same  or  similar  metal,  or  they  are  put  into  a  stone- 
ware basket  (see  fig.  36),  and  then  dipped.  Hooks  and 
strong  rods  of  copper,  brass,  &c.,  of  the  annexed  forms  (see 
nSs-  37?  38)>  are  necessary  for  suspending  articles  upon, 
for  the  purpose  of  dipping  them  into  the  various  liquids. 
It  is  best  that  these  hooks  should  be  of  the  same  material 
as  the  articles,  because  they  are  then  less  liable  to  cause  a 

Y 


322 


The  Art  of  Electro-Metallurgy. 


stain.  Very  small  articles  are  placed  in  a  basket  or  perfo- 
rated bowl,  of  stoneware  or  gutta-percha  (see  fig.  39),  or  a 
tray  of  platinum  wire  gauze  (see  fig.  40),  to  be  dipped. 
Cleaned  ones  of  brass,  are  immersed  in  a  solution  of  argol, 
to  keep  them  from  oxidising.  There  should  also  be  a  series 
of  vessels,  containing  water,  for  effectually  swilling  the  arti- 
cles. The  pans  for  containing  pickling,  dipping,  stripping, 

FIG.  37- 


FIG.  3P. 


FIG. 


FIG.  40. 


and  quicking  liquids,  should  be  of  the  very  best  quality  of 
salt-glazed  stoneware. 

Sometimes,  in  order  to  assist  in  cleaning  the  articles, 
they  are  suspended  for  a  short  time  in  a  suitable  acid  or 
cyanide  liquid,  in  contact  with  the  positive  pole  of  a  battery  ; 
this  dissolves  the  surface,  and  loosens  the  impurities,  unless 


4  Stopping-off'  to  prevent  Deposition.         323 

they  are  very  foul.  In  every  case,  they  should  be  well  rinsed 
with  water,  to  remove  the  adhering  acid,  &c.,  before  dipping 
them  into  the  '  quicking'  solution,  or  immersing  them  in  the 
depositing  vat.  All  objects  which  are  to  have  a  definite 
amount  of  metal  deposited  upon  them,  are  weighed,  and  their 
weight  noted,  after  they  have  been  cleaned. 

'  Stopping-off'  to  prevent  deposition. — Many  articles  which 
are  to  receive  deposits,  require  to  have  portions  of  their  sur- 
face *  stopped-off,'  to  prevent  the  deposit  spreading  over 
those  parts ;  for  instance,  in  taking  a  copy  of  one  side  of  a 
bronze  medallion,  the  opposite  side  must  be  coatedwith  some 
kind  of  varnish,  wax,  or  fat,  to  prevent  deposition  ;  or  in 
gilding  the  inside  of  a  cream-jug  which  has  been  silvered  on 
the  outside,  varnish  must  be  applied  all  round  the  outer  side 
of  the  edge,  for  the  same  reason.  For  gilding  and  other  hot 
solutions,  copal  varnish  is  generally  used ;  but  for  cold  liquids 
and  common  work,  an  ordinary  varnish,  such  as  engravers 
use  for  a  similar  purpose,  will  do  very  well.  In  the  absence 
of  other  substances,  a  solution  of  sealing-wax  dissolved  in 
naphtha  may  be  employed.  (See  also  pp.  182,  226.) 

(  Quicking '  the  surfaces  of  articles. — '  Quicking '  means 
coating  the  surfaces  with  a  film  of  mercury,  for  the 
purpose  of  causing  the  deposited  silver,  &c.,  to  adhere  firmly ; 
the  mercury  acts,  by  offering  a  perfectly  clean  surface  to 
receive  the  deposit,  and,  by  dissolving  to  a  minute  extent, 
both  the  surface  of  the  article,  and  that  of  the  deposit, 
enables  theia  to  mutually  interpenetrate,  and  alloy  with  each 
other. 

Solutions  of  nitrate  or  of  cyanide  of  mercury,  are  used 
for  preparing  the  surfaces  of  copper,  brass,  and  German 
silver,  for  receiving  adhesive  deposits  of  silver.  The  nitrate 
solution  is  prepared,  by  adding  one  ounce  of  mercury  to 
sufficient  nitric  acid,  diluted  with  fhree  times  its  bulk  of  dis- 
tilled water,  to  dissolve  it ;  no  more  mercury  must  be  added 
than  the  liquid  will  take  up  ;  when  completely  dissolved,  add 
about  one  gallon  of  water  (see  also  pp.  143, 166).  To  prepare 


324  The  Art  of  Electro-Metallurgy. 

the  cyanide  solution,  dissolve  one  ounce  of  mercury  as  just 
stated,  dilute  it  with  water,  and  add  a  solution  of  cyanide  of 
potassium  to  it,  exactly  as  long  as  a  precipitate  is  produced  ; 
filter  it,  add  a  small  quantity  of  water  to  the  precipitate  in 
the  filter,  and,  when  thoroughly  drained,  take  out  the  pre- 
cipitate, and  add  to  it,  with  stirring,  a  strong  solution  of 
cyanide  of  potassium,  until  it  is  all  dissolved,  then  add  a 
little  more  cyanide  solution,  and  finally  dilute  it  with  water, 
until  the  whole  measures  one  gallon.  Another  solution  is 
composed  of  one  part  of  pernitrate  of  mercury,  and  two 
parts  of  nitric  or  sulphuric  acid,  dissolved  in  1,000  parts  of 
distilled  water;  or,  take  nitric  acid  of  specific  gravity  i'383, 
add  to  it  half  its  weight  of  mercury,  and  heat  the  liquid 
nearly  to  100°  C.  until  yellow  fumes  are  no  longer  evolved  ; 
the  solution  should  not  be  crystallized  :  dissolve  one  part  by 
weight  of  this  liquid  in  i  ,000  parts  of  water,  with  which  two 
parts  of  sulphuric  acid  have  been  previously  mixed.  Or, 
dissolve  two  ounces  of  mercury  in  two  ounces  of  cold  nitric 
acid,  and  then  add  three  gallons  of  water ;  this  forms  a  good 
solution. 

Almost  any  salt  of  mercury  ('red  precipitate'  for  instance) 
may  be  dissolved  in  a  solution  of  cyanide  of  potassium,  to 
form  a  '  quicking  liquid.'  Such  a  liquid  is  frequently  made, 
by  adding  the  cyanide  to  the  nitrate,  and  not  troubling  to 
wash  the  precipitate.  The  objection  to  a  solution  of  nitrate 
of  mercury  alone  is,  that  as  the  quicking  liquid  cannot  be 
readily  washed  completely  away  from  hollow  articles,  the 
traces  remaining  in  crevices,  cause  the  silver  to  strip  from 
those  parts.  Oxide  of  mercury,  dissolved  in  a  solution  of 
cyanide  of  potassium,  is  often  used  as  a  '  quicking  solution/ 
but  it  is  not  as  good  for  copper  articles,  as  pernitrate  of 
mercury  containing  a  little  hydrochloric  acid.  The  solution, 
when  prepared,  is  kept  in  a  large  stoneware  vessel,  with  a 
pan  of ;  dipping  liquid/  and  two  others  containing  water,  near 
it ;  and  each  placed  near  the  scratch-brush  lathe  and  de- 
positing vats,  in  the  silvering-room. 


1  Quicking'  Articles.  325 

'Quicking  solution'  should  only  contain  sufficient  dis- 
solved mercury,  to  make  a  copper  surface  immersed  in  it  a 
few  seconds,  become  white  ;  if  the  copper  becomes  black, 
the  silver  deposited  upon  it  will  not  adhere ;  it  also  shows 
that  the  solution  of  mercury  is  either  exhausted,  or  not  in  a 
proper  condition.  Too  much  *  quick '  causes  the  silver  to 
1  strip ; '  and  usually  too  little  can  hardly  be  put  on,  but  the 
amount  varies  in  different  cases. 

Articles  which  are  to  receive  a  thick  coating  of  gold  or 
silver,  require  a  stronger  mercurial  solution,  than  those  which 
are  to  receive  a  thin  deposit,  and  they  should  be  perfectly 
white  and  bright  like  silver,  on  coming  out  of  the  mercurial 
bath ;  if  the  '  quicking '  has  succeeded,  they  will  have  an 
uniform  appearance.  The  solution  will  last  a  long  time  ; 
when  it  gets  nearly  exhausted,  it  is  liable  to  turn  the  articles 
which  are  dipped  into  it,  of  a  dark  colour;  it  is  then  better 
to  prepare  a  fresh  liquid,  than  to  revive  the  old  one. 

All  articles,  while  still  wet  from  the  cleaning  and  quicking 
processes,  should  be  quickly  immersed  into  the  depositing 
vat.  The  practical  minutise  of  preparing  the  surfaces  of 
different  metals,  for  receiving  adhesive  deposits,  vary  in 
almost  every  manufactory,  and  much  information  yet  remains 
to  be  developed  upon  this  point ;  for  want  of  this  knowledge, 
the  most  skilful  operators  sometimes  fail  in  producing  perfect 
adhesion,  especially  upon  zinc,  cast  iron,  steel,  and  Britannia 
metal. 

Wireing  articles. — The  articles  have  wires  of  copper 
attached  to  them,  to  suspend  them  by  when  in  the  vat.  The 
wires  differ  in  size ;  with  small  objects,  such  as  spoons, 
knives,  forks,  snuffers,  teapots,  jugs,  &c,  size  No.  20  or  22  of 
the  Birmingham  wire  guage5  and  about  eighteen  or  twenty 
inches  long,  are  used ;  very  large  ones,  such  as  fire-irons, 
fenders,  hat-stands,  and  pieces  of  ornamental  iron-work,  are 
suspended  by  strong  copper  or  brass  hooks.  In  some  cases, 
where  a  powerful  and  certain  connection  is  required,  the 
wires  are  soldered  to  the  articles. 


326  The  A  rt  of  Electro-Metallurgy. 

Voltaic  batteries. — There  are  but  few  kinds  of  voltaic 
batteries  usually  employed  in  electro-metallurgy,  and  those 
which  are  used,  are  not  often  employed  for  operations  of 
the  greatest  magnitude;  in  such  cases,  magneto-electric 
machines  are  rapidly  superseding  voltaic  batteries,  because 
they  furnish  electricity  at  much  less  expense,  and  their  action 
is  more  uniform.  I  shall,,  therefore,  only  briefly  describe  such 
as  have  been  commonly  employed. 

Those  most  used  in  electro-deposition  are,  the  old  Wol- 
laston  battery  of  zinc  and  copper  plates  in  dilute  sulphuric 
acid,  Smee's,  DanielPs,  Bunsen's,  and  Grove's. 

Wollastoris  battery. — The  one  which  has  been  most  em- 
ployed for  electro-deposition  upon  the  large  scale,  is  repre- 
F  sented  in  fig.  41.    In  consists  of  a  large  stone- 

ware jar,  nearly  filled  with  a  mixture  of  about 
ten  parts  of  water  and  one  of  oil  of  vitriol 
Across  the  top  of  the  jar,  is  a  moveable  bar  of 
well  varnished  wood,  with  a  longitudinal  and 
vertical  groove  in  it,  within  which  a  thick  plate 
of  zinc  may  be  raised  and  lowered,  by  means 
of  a  weight  with  a  cord  passing  over  a  pulley: 
the  great  use  of  this  is,  to  regulate  the  quantity 
of  the  current  To  the  edges  or  sides  of  the 
bar  are  fixed  two  sheets  of  copper,  connected 
together  by  a  copper  band  at  their  corners,  and 
so  attached,  that  they  may  be  occasionally  re- 
moved and  cleansed;  they  extend  nearly  to  the  bottom  of 
the  liquid.  Vertical  rods  of  varnished  wood,  are  fixed  upon 
the  under  surface  of  the  cross-bar,  to  prevent  the  zinc  touch- 
ing the  copper.  The  copper  plates  should  not  be  allowed 
to  remain  many  hours  in  the  liquid,  when  the  battery  is  not 
in  action,  because  they  then  corrode,  and  form  a  small  amount 
of  cupric  sulphate,  which  dissolves  in  the  liquid,  and  this  acts 
upon  the  zinc  plates,  and  causes  them  to  waste  rapidly,  because 
the  zinc  precipitates  the  copper  upon  itself,  and  thus  a  local 
battery  is  formed.  If  the  copper  plates  remain  long  in  the 


Voltaic  Batteries.  327 

air  in  a  wet  acid  state,  they  become  covered  with  a  badly 
conducting  blackish  film  of  oxide,  and  should  be  scrubbed 
with  sand  and  a  hard  brush,  and  washed  before  being  again 
used. 

Smee's  battery. — This  one  has  been  extensively  used  for 
small  operations,  and  is  very  convenient.  It  consists  of 
amalgamated  zinc  and  platinized  silver,  immersed  in  dilute 
sulphuric  acid  ;  and  is  usually  of  the  form  shown  by  fig.  42. 
Two  plates  of  zinc  z  z  are  held  together  (with  a  bar  of  var- 
nished wood  between  them),  by  means  of  FIG 
a  clamp  binding-screw  (see  fig.  50,  p.  335), 
and  the  sheet  of  platinized  silver  s,  is 
fixed  in  a  groove  in  the  under  side  of  the 
wooden  bar,  and  attached  to  a  pillar  bind- 
ing-screw (see  fig.  46,  p.  335).  The  silver 
and  zinc  are  prevented  from  mutual  con- 
tact, by  means  of  pieces  of  cork  placed 
between  them  at  their  lower  ends.  It  is 
important  in  this  battery  (and  to  a  less 
extent  in  that  of  Wollaston)  that  the  sul- 
phuric acid  employed  should  be  free  from 
nitric  acid;  also  that  the  negative  plate 
should  not  come  into  contact  with  mercury.  Platinized 
silver  (i.e.  silver  coated  with  black  platinum  in  a  state  of 
very  fine  division)  is  much  more  effective  than  silver  alone, 
because  with  the  latter  metal,  the  bubbles  of  hydrogen 
evolved,  adhere  to  its  surface,  and  diminish  the  action, 
whilst  with  platinized  silver  they  escape  to  the  surface  of  the 
liquid  rapidly.  Platinized  silver  is  also  more  electro-negative 
than  silver  alone,  and  still  more  so  than  copper,  and  therefore 
produces  a  stronger  current.  The  mode  of  platinizing  has 
already  been  described  (see  p.  118). 

Daniel? s  battery.  —  This  one  has  also  been  largely  used 
in  electro-deposition,  but  its  use  for  that  purpose  has  dimi- 
nished. It  consists  essentially  of  amalgamated  zinc  in  dilute 
sulphuric  acid,  and  copper  in  a  nearly  saturated  solution  of 


328 


The  A  rt  of  Electro-Metallurgy. 


FIG.  43- 


cupric  sulphate,  the  two  liquids  being  prevented  from  mixing 
(but  allowed  to  touch  each  other)  by  means  of  a  porous  par- 
tition. One  of  its  forms  is  that  shown  in  fig.  43,  in  which 
c,  is  a  copper  vessel  forming  the 
negative  metal,  and  containing  the 
cupric  solution,  and  z,  a  bar  of  cast 
zinc,  supported  in  the  acid  and  water 
within  the  porous  cell,  by  the  wooden 
lid  of  that  vessel.  The  copper  cell 
has  a  large  lip  L,  which  is  kept  full 
of  crystals  of  blue  vitriol,  to  supply 
the  loss  of  copper  deposited  upon 
the  vessel  ;  it  may  also  be  used  for 
the  purpose  of  pouring  out  the  solu- 
tion. 

The  great  advantage  of  this  battery,  is  the  uniformity  of 
its  action,  and  it  is  therefore  called  the  '  constant '  battery. 
FIG.  44.     It  is  sometimes  constructed  with  the  acid  and 
water  outside,  and  the  copper  plate  and  solution 
inside ;   in  that  case  a   cylinder  of  rolled  plate 
zinc  is  employed;  it  is  also  occasionally  made  of 
a  rectangular  form,  with  the  porous  cell  of  a  flat 
shape. 

Bunseris  battery. — This  kind  is  often  em- 
ployed for  gilding,  two  or  three  large  cells  being 
commonly  used.  It  consists  of  amalgamated 
plate  zinc  in  dilute  sulphuric  acid,  and  gas-carbon 
or  Bunsen's  coke,  in  strong  nitric  acid ;  the  latter 
liquid  being  in  a  porous  cell.  The  gas-carbon 
is  usually  in  the  form  of  thick  rectangular  bars, 
and  in  such  cases  the  nitric  acid  is  in  a  cylin- 
drical porous  cell;  but  sometimes  it  is  in  the  form 
of  plates,  and  flat  porous  cells  are  then  necessary.  As 
the  carbon  is  a  porous  substance,  the  acid  rises  in  it  by 
capillary  action,  and  corrodes  the  metallic  connections;  the 
most  effectual  way  of  obviating  this,  is  by  using  very  long 


Relative  Strength  of  Batteries.  329 

pieces  of  the  substance,  a  considerable  portion  of  each  piece 
being  out  of  the  liquid,  and  putting  a  coating  of  varnish 
or  paraffin  upon  them  a  little  way  down.     Sometimes,   in 
order  to  form  a  more  secure  connection,  the  upper  end  of 
the  bar  is  coated  with  copper  by  electro-deposition ;  or  else 
it  is  encased  with  metal  by  dipping  it  into  melted 
lead.    Fig.  44  shews  a  bar  of  carbon  with  its  bind-     FlG' 45< 
ing  screw  attached. 

Graves  battery  is  precisely  similar  to  Bunsen's 
in  its  essential  parts,  except,  that  it  has  platinum 
instead  of  carbon.  The  nitric  acid  and  sheet  of 
platinum,  are  contained  in  narrow  flat  porous  cells 
of  the  form  shewn  in  fig.  45.  It  is  one  of  the 
strongest  of  batteries,  but  emits  noxious  acid 
fumes  after  having  been  some  time  in  action,  and 
its  power  soon  declines. 

Relative  strength  of  batteries. — The  electro-motive  force,  or 
power  of  overcoming  resistance  (see  p.  70),  varies  in  different 
batteries,  and  is,  according  to  Latimer  Clarke,  as  follows  : — 


Smee's  (when  in  action)  about  25 
Wollaston's(copperand  zinc 
in  dilute  acid)         .         .     46 


Grove's  ....  100 
Bunsen's  .  .  .  .98 
Daniell's  .  .  .  .  56 
Smee's  (when  not  in  action)  57 

(See  «  Electrical  Measurement,'  p.  108,  by  L.  Clarke). 

From  this  table  it  will  be  observed,  that  the  strength  of  a 
Smee's  cell  decreases  during  its  working ;  this  occurs  very 
quickly  after  the  current  commences,  because  the  internal 
resistance  is  increased  by  hydrogen  gas  adhering  to  the 
negative  plate;  after  that  has  occurred,  the  current  remains 
tolerably  constant;  a  similar  phenomenon  happens  with  the 
Wollaston's  element,  but  not  with  the  Daniell's,  because  in 
the  latter,  the  negative  surface  is  kept  free  from  that  gas. 

Relative  advantages  of  different  batteries. — Wollaston's 
is  the  most  suitable  one  in  cases  where  the  resistance  is  not 
great,  and  where  a  large  quantity  of  electricity,  and  long-con- 


3  3 o  TJie  A  rt  of  Electro-Metallurgy. 

tinued  action  (as  in  depositing  copper  and  silver)  are  re- 
quired, because  its  electro-motive  force  is  small ;  its  action 
(after  once  it  has  commenced)  is  tolerably  uniform,  and  large 
plates,  and  considerable  bulks  of  exciting  liquid,  may  be  con- 
veniently employed.  Smee's  is  suitable  for  similar  cases,  but 
where  only  a  small  quantity  of  electricity  is  required,  because 
large  plates  of  platinized  silver  are  expensive.  Daniell's  is 
the  best  in  cases  where  the  resistance  is  greater,  and  a  very 
uniform  current  is  necessary.  Grove's  and  Bunsen's  are  the 
most  suitable  where  the  resistance  is  still  greater,  and  an  occa- 
sional current  of  considerable  electro-motive  force,  but  not 
of  long  continuance,  is  necessary,  as  in  gilding,  and  pre- 
paring for  gilding  (i.e.  brassing  or  coppering)  small  articles  of 
iron,  steel,  &c.  in  cyanide  solutions. 

Exciting  liquids  for  batteries. — In  all  these  batteries,  the 
zinc  element  is  immersed  in  dilute  sulphuric  acid.  The 
strength  employed  of  this  mixture,  varies  from  one  measure 
of  acid  and  fifty  of  water,  to  one  of  acid  and  five  of  water; 
the  usual  strength  with  batteries  such  as  Grove's  and 
Bunsen's  (which  are  soon  exhausted),  is  one  to  five,  but  with 
Daniell's,  Smee's,  or  Wollaston's,  one  to  ten  or  twenty  is  a  very 
good  proportion.  The  price  of  concentrated  sulphuric  acid 
(oil  of  vitriol)  is  about  three -halfpence  per  pound.  It  is  impor- 
tant that  this  liquid  be  free  from  nitric  acid  (which  it  some- 
times contains),  because  that  acid  wastes  the  zinc,  and  in 
Smee's  battery  also  corrodes  the  silver.  To  test  for  nitric 
acid,  add  to  the  suspected  liquid,  a  small  quantity  of  a  solu- 
tion of  indigo  in  pure  sulphuric  acid,  and  boil  the  mixture ; 
if  the  colour  of  the  indigo  does  not  disappear,  nitric  acid  is 
not  present.  If  the  silver  plates  in  a  Smee's  battery,  become 
covered  with  a  dirty  whitish  film,  a  trace  of  nitric  acid  is 
probably  present.  The  nitric  acid  used  in  Grove's  battery, 
should  be  free  from  hydrochloric ;  otherwise,  when  it  gets 
warm  by  the  action  of  the  battery,  it  will  corrode  and 
dissolve  a  little  of  the  platinum  plates.  To  ascertain  if 
hydrochloric  acid  is  present,  dilute  some  of  it  with  dis- 


Liquids  for  Batteries.  331 

tilled  water,  and  add  two  drops  of  a  solution  of  nitrate  of 
silver  :  if  a  white  cloud,  or  milkiness  appears,  that  acid  is 
present.  Common  oil  of  vitriol  nearly  always  contains 
sulphate  of  lead  dissolved  in  it,  and  when  one  measure 
of  the  acid  is  added  to  five  or  ten  measures  of  water,  the 
mixture  becomes  cloudy,  and  a  greyish  white  powder  (con- 
sisting of  the  sulphate)  settles  to  the  bottom  of  the  vessel ; 
this  powder  should  not  be  allowed  to  get  into  the  battery 
cells,  otherwise  it  will  settle  upon  the  zinc  plates,  and  cause 
them  to  waste.  In  mixing  oil  of  vitriol  and  water,  it  is  highly 
important  that  the  acid  should  be  gradually  added  to  the 
water  and  not  the  reverse,  and  also  that  the  mixture  be  stirred 
during  the  addition ;  and  it  is  especially  necessary,  that  the 
water  and  acid  be  cold,  because  great  heat  is  evolved  by 
mixing  them  ;  if  water  be  added  to  oil  of  vitriol,  an  explosion 
may  be  produced  by  the  heat ;  and  more  especially  is  it 
dangerous  to  add  hot  water  to  oil  of  vitriol.  Brown  oil  of 
vitriol  is  that  which  has  been  made  from  iron-pyrites  obtained 
from  the  coal  measures,  and  its  colour  is  due  to  particles  of 
carbon ;  it  is  sometimes  also  impure ;  but  even  the  purest 
sulphuric  acid  is  occasionally  brown,  from  particles  of  organic 
dust  getting  into  it.  Strong  sulphuric  acid  has  a  specific 
gravity  of  i  '845  ;  if  its  gravity  is  less  than  this,  it  contains 
water.  If  the  acid  used  in  a  battery  is  not  sufficiently  dilu- 
ted, crystals  of  sulphate  of  zinc  are  apt  to  form  upon  the 
bottom  ends  of  the  zinc  plates  after  a  time,  through  want 
of  water  to  dissolve  them,  and  this  impedes  the  current; 
a  mixture  of  ten  parts  by  measure  of  water  to  one  of  acid,  is 
sufficiently  dilute  to  prevent  this;  such  a  mixture  has  a  specific 
gravity  of  about  no. 

The  only  other  liquid  used  in  the  batteries  I  have  de- 
scribed, is  a  solution  of  sulphate  of  copper ;  this  salt  is 
usually  sufficiently  pure,  if  a  proper  price  (about  sixpence 
per  pound)  is  paid  for  it.  Any  green  colour  in  it,  is  in- 
dicative of  the  presence  of  sulphate  of  iron,  with  which  the 
cheaper  varieties  are  contaminated. 


332  The  A  rt  of  Electro-Metallurgy. 

Amalgamation  of  zinc. — Zinc  rods  and  plates  are  always 
amalgamated,  because  it  makes  them  more  electro-positive 
(see  p.  63),  and  because  it  also  largely  protects  them  from 
corrosion  when  the  battery  is  not  in  action.  The  explanation 
of  this  is  not  very  clear,  but  it  probably  is,  that  the  mercury, 
by  dissolving  the  surface  of  the  zinc,  and  traces  of  foreign 
metals  in  it,  renders  the  whole  of  that  surface  of  uniform 
composition,  and  therefore  no  one  part  of  it  is  relatively 
electro-positive  or  negative  to  another,  and  no  local  current 
can  be  generated.  It  is  however  dependent  also  upon  the 
presence  of  a  film  of  hydrogen  upon  the  surface  of  the  metal, 
for  if  a  trace  of  nitric  acid,  or  other  liquid  capable  of  oxi- 
dizing or  removing  such  a  film,  is  present,  the  mercury  does 
not  protect  the  zinc. 

Zinc  rods  or  plates  may  be  well  amalgamated,  by  immers- 
ing them  in  dilute  sulphuric  acid  until  gas  is  freely  evolved, 
then  pouring  mercury  upon  them,  and  rubbing  them  until 
they  are  bright  all  over.  If  the  plates  are  new,  they  are 
probably  greasy  from  the  process  of  rolling,  and  should  first 
be  dipped  in  the  caustic  potash  solution  and  swilled,  before 
putting  them  into  the  acid,  or  they  should  be  scraped.  After 
having  been  amalgamated,  they  should  be  placed  on  their 
ends  to  drain  off  the  superfluous  mercury,  and  then  the  re- 
siduary mercury  wiped  off  them.  Ruhmkorff  amalgamates 
zinc  plates,  by  dipping  them  into  a  solution  made  as  fol- 
lows : — Dissolve  one  part  of  mercury  in  five  parts  of  aqua 
regia  (i.e.  one  part  of  nitric  and  three  of  hydrochloric 
acids),  and  then  add  five  parts  of  hydrochloric  acid.  An- 
other plan,  is  to  put  some  mercury  into  a  coarse  flannel  bag, 
dip  the  bag  occasionally  into  dilute  hydrochloric  acid,  and 
rub  it  upon  the  zinc  plate  or  rod. 

Roseleur  uses  an  amalgamating  salt,  prepared  by  boiling 
an  aqueous  solution  of  mercuric  nitrate,  with  an  excess  of 
a  powder,  composed  of  equal  parts  of  mercuric  chloride  and 
mercuric  sulphate,  cooling  the  mixture,  and  using  the  liquid 
only.  The  liquid  is  added  to  the  mixture  of  sulphuric  acid 


A  malga  mat  ion  of  Zinc  Plates.  333 

and  water,  in  those  batteries  only  where  two  liquids  are  em- 
ployed. 

The  mercury  used  for  amalgamating  should  be  pure ; 
if  it  contains  tin,  lead,  bismuth,  or  copper,  &c.,  these  metals 
will  adhere  to  the  zinc,  and  cause  great  waste,  by  what  is 
termed  '  local  action/  which  means,  that  the  zinc  and  the 
particles  of  foreign  metal,  being  in  contact  in  an  acid  liquid, 
constitute  a  multitude  of  little  voltaic  couples,  which  gene- 
rate electric  currents  (by  corrosion  of  the  zinc  and  waste 
of  the  acid),  when  the  principal  current  is  not  circulating. 
For  a  similar  reason,  the  zinc  also  should  be  free  from 
metals  less  positive  than  itself.  New  zincs  require  frequent 
amalgamation,  because  the  mercury  soaks  into  them,  but  as 
they  get  old  and  thin  by  use,  this  mercury  is  left  upon  their 
surface,  and  therefore  they  rarely  need  to  be  amalgamated. 
When  zinc  plates  become  so  .thin  as  to  fall  to  pieces  on 
handling,  new  ones  should  be  substituted,  and  the  old  ones 
may  be  melted,  and  cast  into  rods  for  Darnell's  batteries  ; 
or  be  broken  up,  put  in  an  iron  retort,  and  the  mercury  dis- 
tilled from  them  at  a  strong  red  heat,  through  a  wide  and 
wet  tube  of  leather,  into  a  vessel  of  water. 

Selection  of  zinc  for  batteries. — The  best  kind  of  zinc  for 
batteries,  and  the  kinds  chiefly  in  use  by  electro- platers,  are 
the  Belgian  and  Silesian.  The  thickness  of  the  plates  should 
vary  with  the  size  of  the  battery ;  the  smallest  should  not  be 
much  less  than  one-eighth  of  an  inch  thick,  on  account  of  its 
brittleness  when  amalgamated  ;  large  ones  are  generally  about 
three-sixteenths  or  one-quarter  of  an  inch  in  thickness.  Zinc 
bolts  for  DanielPs  batteries  are  sometimes  made,  by  melt- 
ing together  a  number  of  old  worn-out  pieces  of  battery 
plates,  and  casting  in  a  suitable  mould.  The  wholesale  price 
of  unrolled  (cake)  zinc,  is  usually  from  twenty  to  thirty 
shillings  per  hundredweight.  As  all  zinc  contains  traces  of 
less  positive  metals;  when  the  former  dissolves  away,  the 
latter  come  to  the  surface,  and  form  an  amalgam,  and 
diminish  the  protective  power  of  the  mercury;  such  a  coating 


334  The  A  rl  of  Electro-Metallurgy. 

should  occasionally  either  be  scraped  off,  or  removed  by 
means  of  a  very  hard  brush,  and  pure  mercury  applied.  Cast 
zinc  is  not  so  good  for  electrical  purposes  as  rolled  zinc  •  it 
is  also  less  easy  to  amalgamate.  Plate  zinc  may  be  cut  by 
means  of  a  saw  with  fine  teeth,  or  by  drawing  a  line  across 
it  repeatedly  (using  great  pressure),  with  the  end  of  a  tri- 
angular file  which  has  been  ground  to  a  sloping  point.  It 
may  also  be  bent  into  cylinders  whilst  it  is  hot. 

Battery  cells.—  These  are  either  of  stoneware,  glass,  gutta- 
percha,  or  ebonite.  For  large  cells,  stoneware  is  nearly 
always  employed  :  for  small  ones,  glass  is  very  good,  and  so 
is  gutta-percha,  but  the  preference  is  generally  given  to 
ebonite,  especially  for  Grove's  battery,  because  it  is  not 
brittle  like  glass,  and  does  not  become  softened  like  gutta- 
percha  by  the  heat  generated  in  the  battery. 

Porous  cells  for  batteries. — These  vary  very  greatly  in 
quality :  some  are  so  slightly  porous,  that  they  very  seriously 
hinder  the  passage  of  the  electricity ;  most  excellent  ones  are 
manufactured  by  Messrs  Wedgwood  &  Co.  Formerly,  porous 
cells  of  wood  were  employed,  but  now,  only  those  of  earth- 
enware are  used  ,  they  should  always  be  kept  in  clean  water 
when  not  in  use,  to  remove  nitric  acid  and  salts  of  the  bat- 
tery liquids  from  them,  to  prevent  their  cracking,  and  to 
preserve  them  always  fit  for  immediate  use.  The  degree 
of  porosity  of  two  cells  may  be  compared  by  drying  them, 
and  then  simultaneously  filling  them  with  water,  and  observing 
the  appearance  of  their  outer  surfaces  after  one  or  two 
minutes. 

Binding-screws.  —  These  are  employed  for  connecting 
and  holding  together  the  plates,  connecting  wires,  &c.  of  a 
battery.  That  shown  by  fig.  46  is  for  attaching  to  the  wooden 
cross-bar  and  platinized  silver  plate  of  a  Smee's  cell ;  47  and 
48  are  for  attaching  to  zinc  or  copper  plates ;  49  is  for  join- 
ing zinc  and  platinum,  or  zinc  and  copper  plates  together  ; 
50  is  for  attaching  to  the  top  of  a  thick  bar  of  carbon,  or 
for  holding  together  the  zinc  plates  of  a  Smee's  battery; 


Management  of  Batteries. 


335 


and  51  is  a  screw  I  have  devised  and  employed  for  joining 
together  the  ends  of  copper  wires. 


FIG.  46. 


FIG.  47- 


FIG.  48. 


FIG.  49. 


FIG.  50. 


FIG.  51. 


sO 


Management  of  batteries. — If  the  acid  liquid  in  contact 
with  the  zinc  is  very  strong,  the  zinc  plates  require  frequent 
watching,  to  see  that  there  is  no  local  action,  and  when  gas 
is  seen  or  heard  rising  from  them,  or  when  any  dull  patches 
appear  upon  them,  where  the  acid  has  acted  too  strongly, 
they  should  be  amalgamated  ;  if  this  is  neglected,  great  holes 
will  be  quickly  corroded  in  them.  They  should  be  taken 
out  of  the  cells  every  evening,  if  the  acid  liquor  is  at  all 
strong,  unless  deposition  is  required  to  continue  all  night. 

After  a  Wollaston's,  Smee's,  or  DanielPs  battery,  has  been 
at  work  a  few  days,  a  small  amount  of  sulphuric  acid  should 
be  added,  and  the  liquid  stirred,  and  this  should  be  done  as 
often  as  the  current  becomes  feeble,  until  at  length  the  liquid 
acquires  an  oily  consistence,  and  becomes  nearly  saturated 
with  zinc  salt,  which  crystallizes  upon  the  cells  and  plates 


336  TJte  A  rt  of  Electro-Metallurgy. 

above  the  surface  of  the  liquid ;  it  is  then  time  to  remove 
the  liquid,  and  charge  the  battery  afresh.  If  crystals  of  sul- 
phate of  zinc  are  required  for  depositing  or  other  purposes, 
the  exhausted  solution  may  be  set  aside,  and  allowed  to 
evaporate.  Sometimes  in  a  Smee's  or  Wollaston's  battery,  a 
deposit  of  zinc  forms  upon  some  of  the  negative  plates ;  when 
this  happens,  it  is  a  sign  that  the  acid  is  exhausted  in  those 
cells  ;  either  more  acid,  or  a  fresh  mixture,  should  then  be 
put  in  ;  the  deposit  may  also  be  removed,  by  immersing  the 
negative  plates  in  a  separate  portion  of  dilute  sulphuric 
acid. 

Great  care  must  be  taken,  that  no  mercury  comes  into 
contact  with  the  plates  of  copper  or  platinized  silver,  the  latter 
especially,  as  it  makes  them  brittle,  and  greatly  diminishes 
the  electric  power.  To  remove  mercury  from  copper  plates, 
the  latter  should  be  heated  to  redness,  but  with  silver  plates, 
a  much  less  heat  should  be  applied  for  a  longer  time,  and 
then  the  plates  should  be  re-platinized.  Copper  plates  should 
be  frequently  scoured  with  sand  with  a  hard  brush  ;  and  the 
silver  plates  should  be  re-platinized  when  they  become  light 
in  colour,  which  will  happen  after  about  six  months'  careful 
working. 

In  managing  a  Grove's  or  Bunsen's  battery,  it  is  highly 
important,  not  to  allow  any  of  the  nitric  acid  to  get  into  con- 
tact with  the  zinc,  because  it  produces  strong  local  action,  and 
waste  of  that  metal.  As  the  nitric  acid  cannot  be  prevented 
from  passing  through  the  porous  divisions,  such  batteries  can- 
not be  kept  in  continual  energetic  action  more  than  a  day,  in 
consequence  of  this  circumstance.  The  porous  cells  of  such 
batteries  should  be  soaked  in  water,  the  water  being  changed 
twice  or  three  times  (so  as  to  extract  all  the  nitric  acid  from 
them),  before  they  are  used  a  second  time ;  therefore,  for  con- 
tinual use  of  such  a  battery,  two  or  three  sets  of  such  cells 
are  necessary,  some  being  in  soak  whilst  others  are  in  use. 
In  charging  any  two-liquid  batteries,  it  is  best  to  have  the 
liquids  level,  and  if  they  be  either  Grove's,  Bunsen's,  or 


Regulation  of  Electric  Power.  337 

Daniell's,  the  liquid  in  the  zinc  division  should  be  rather  the 
higher. 

It  is  best  to  employ  separate  batteries  for  each  different 
depositing  liquid.  Each  battery  should  be  tested  before  it  is 
used :  this  may  be  done  in  a  rough,  though  usually  sufficiently 
accurate  way  for  the  purpose,  if  the  current  is  a  strong  one, 
by  connecting  one  end  of  the  battery  to  a  file,  and  drawing 
the  point  of  the  wire  from  the  other  end  of  the  battery 
along  its  surface  ;  by  the  degree  of  brilliancy  of  the 
sparks  produced,  the  strength  of  the  current  can  be  estima- 
ted. Before  testing  or  using  a  battery,  it  is  necessary  to 
examine,  and  see  that  all  the  points  of  contact  of  the  wires, 
screws,  &c.  are  clean,  and  that  the  screws  hold  the  wires 
firmly ;  it  is  also  advisable  to  see  that  all  the  cells  are  con- 
nected in  the  right  order,  for  if  only  one  cell  is  connected 
the  opposite  way,  it  will  not  only  be  rendered  ineffective,  but 
will  also  neutralize  the  action  of  one  of  the  others ;  and  its 
negative  plate  will  be  liable  to  dissolve  by  the  influence  of 
the  current  from  the  remaining  cells.  Voltaic  batteries 
should  be  kept  in  a  place  of  moderate  and  uniform  tem- 
perature; not  where  the  liquids  are  liable  to  freeze,  or  rapidly 
evaporate. 

Regulation  of  electric  power. — This  is  always  a  matter  of 
considerable  importance,  especially  when  depositing  from 
solutions,  which  will  not  bear  a  great  range  of  electric  force, 
without  spoiling  the  quality  of  the  deposited  metal.  It  may 
be  effected  in  a  variety  of  ways,  viz.,  by  making  alterations 
either  in  the  battery,  in  the  depositing  vessel,  or  in  the  wires 
connecting  them.  The  electro-motive  force  (commonly  called 
1  the  intensity  ')  of  the  current  may  be  increased,  by  adding 
to  the  number  of  cells  in  the  battery ;  or  by  using  cells  of 
greater  intrinsic  pushing  power,  for  instance  Grove's  instead  of 
Smee's,  &c.  (see  p.  327).  As  the  electro-motive  force  is  dimin- 
ished by  resistance,  a  diminution  of  resistance  in  any  part  of 
the  circuit  will  increase  it ;  this  may  be  effected  to  a  certain 
extent  by  making  the  depositing  liquid  hot,  using  larger 

z 


338  The  Art  of  Electro-Metallurgy. 

electrodes,  or  placing  them  nearer  together.  The  quantity 
of  the  current  may  be  increased  by  all  these  means,  and  also 
by  immersing  the  battery  plates,  or  only  one  of  them,  deeper 
in  the  liquid.  The  usual  method,  however,  for  regulating  the 
electro-motive  force  of  the  current,  is  to  alter  the  number  of 
cells  in  the  battery ;  and  for  regulating  the  quantity,  to  alter 
the  depth  of  immersion  of  one  of  the  battery  plates  (see 
p.  326);  but  sometimes  the  latter  cannot  be  conveniently 
effected,  and  in  that  case,  the  anode  is  either  increased,  or 
diminished  in  size.  As  that  also  is  usually  inconvenient,  a 
large  piece  of  copper  or  brass  is  sometimes  suspended  to  act  as 
a  cathode  along  with  the  article  to  be  coated,  and  thus  relieve 
it  of  part  of  the  current.  Galvanometers  or  voltameters 
(see  p.  73)  are  very  rarely  employed  to  measure  the  electric 
currents  employed  in  practical  electro-deposition,  chiefly, 
because  the  want  of  such  instruments  is  not  felt,  and  partly, 
because  the  processes  are  too  coarse  for  the  use  of  delicate 
apparatus. 

Compound  voltaic  batteries  are  usually  so  constructed, 
that  they  may  be  used  to  supply  either  a  current  of  less 
quantity  and  greater  electro-motive  force,  or  the  reverse. 
By  connecting  a  series,  say  of  twelve  cells,  all  in  one  row, 
with  the  metals  alternating  throughout,  we  obtain  from  the 
end  wires,  a  current  of  a  quantity  of  one,  and  an  electro- 
motive force  of  twelve.  By  connecting  them  as  a  double 
row  or  series  of  six,  the  two  end  zincs  being  connected  to 
one  terminal  wire,  and  the  two  end  coppers  to  the  other,  we 
get  a  current  of  a  quantity  of  two,  and  electro -motive  force 
of  six.  By  connecting  them  in  a  similar  way  in  a  treble  row 
as  a  series  of  four,  we  obtain  a  current,  the  quantity  of  which 
is  equal  to  three,  and  the  electro-motive  force  equal  to  four. 
By  arranging  them  in  a  quadruple  row,  and  a  series  of  three, 
we  get  a  quantity  of  four,  and  electro-motive  force  of  three. 
By  placing  them  as  a  sextuple  row,  and  as  a  series  of  two, 
we  get  a  quantity  of  six,  and  electro-motive  force  of  two. 
And  finally  by  placing  them  in  single  row,  connecting  all  the 


Selection  of  Depositing  Processes.  339 

zincs  together  by  one  wire,  and  all  the  silvers  by  another, 
they  all  act  as  one  pair  of  twelve  times  the  surface  of  a  single 
cell,  and  we  obtain  a  quantity  of  twelve,  and  electro-motive 
force  of  one.  To  make  such  arrangements  successfully,  it  is, 
however  necessary,  that  all  the  plates  be  provided  with  suit- 
able screws,  also  that  all  the  cells  be  of  a  similar  kind,  and 
equal  in  electro-motive  force,  otherwise  the  currents  from  the 
stronger  ones  will  be  liable  to  pass  partly  through  the  weaker 
ones  instead  of  through  the  plating  solution,  and  also  per- 
haps damage  the  battery,  by  causing  some  of  the  negative 
plates  to  be  corroded  ;  it  is  therefore  only  occasionally  that 
batteries  are  so  arranged,  i.e.,  not  in  single  alternate  series. 
The  power  of  the  current  from  magneto-electric  machines,  is 
usually  regulated  by  interposing  a  piece  of  thin  iron  wire  in 
the  circuit. 

Selection  of  depositing  processes. — Different  articles  are 
electro- coated  by  different  methods  ;  some  are  coated,  as  al- 
ready stated,  by  simple  immersion,  others  by  simple  contact 
with  zinc,  and  others  by  means  of  a  separate  current ;  but 
an  electro-plater  usually  employs  only  the  latter  method. 
For  very  small  articles  of  which  there  are  a  great  number, 
such  as  buttons,  hooks  and  eyes,  pins,  &c.,  and  which 
require  only  a  very  thin  deposit,  the  simple  immersion  or 
wash  process  answers  very  well,  being  both  easy  of  exe- 
cution, and  cheap.  But  for  all  ordinary  deposits,  plating, 
&c.,  the  separate  current  method  is  by  far  the  best,  because 
coatings  of  greater,  and  of  sufficient  thickness,  of  all  ordi- 
nary metals,  may  be  obtained  by  it,  and  the  solutions  do  not 
usually  (as  in  the  other  processes)  require  renewal. 

'  Pyro  plating? — A  process  termed  '  pyro-plating '  has 
during  the  last  few  years  been  introduced,  and  is  stated  to 
be  specially  suited  for  causing  a  coating  of  gold,  silver, 
platinum,  copper,  nickel,  brass,  bronze,  or  aluminium- 
bronze,  to  adhere  to  metals,  in  cases  where  the  metals  to  be 
plated,  will  not  readily  receive  a  film  of  mercury  by  the 

z  2 


340  The  Art  of  Electro-Metallurgy. 

ordinary  '  quicking '  process,  as  with  iron,  steel,  nickel,  and 
aluminium. 

The  article  of  iron,  steel,  &c.,  is  first  made  perfectly 
clean,  by  immersion  in  a  boiling  solution  of  caustic  alkali, 
then  brushed  with  emery,  also  with  a  steel  brush  in  a  stream 
of  solution  of  washing  soda ;  then  suspended  in  a  similar 
solution  ;  next  made  the  cathode  in  a  hot  solution  of  caustic 
alkali,  with  a  strong  current  to  evolve  from  it  plenty  of  hydro- 
gen, until  its  surface  looks  '  silvery  ; '  and  then  transferred  to 
a  special  solution  of  silver,  and  plated.  A  previously 
weighed  metal  plate,  of  equal  amount  of  surface,  is  immersed 
as  a  cathode  by  its  side,  and  weighed  from  hour  to  hour, 
until  sufficient  silver  has  been  deposited.  The  original 
article  is  then  removed  from  the  vat,  and  (after  washing  ?) 
heated  in  a  furnace  to  '  drive  '  the  coating  of  silver  (or  other 
metal  as  the  case  may  be),  into  its  surface  ;  and  if  the 
article  requires  tempering,  it  is  quenched  in  water.  Pyro- 
gilding  is  performed  in  a  similar  way  to  pyro-silvering,  except 
that  the  whole  of  the  metal  is  not  put  on  at  once,  but  in 
three  successive  layers,  and  heated  in  the  furnace  after 
each  coating.  The  first,  before  being  heated,  looks  per- 
fect, but  by  the  heating,  the  gold  nearly  all  disappears, 
being  driven  into  the  under  metal.  The  second,  only  partly 
disappears  by  the  influence  of  the  heat ;  and  the  third 
entirely  remains.  Pyro-gilding  is  specially  recommended  for 
coating  articles  of  iron  and  steel  ('Chemical  News/  vol.  xxvi. 
pp.  26  and  173). 

Selection  of  depositing  liquids. — The  most  important 
points  to  be  observed,  in  selecting  a  liquid  for  the  separate 
current  process,  are  :  first,  that  it  should  yield  its  metal  freely, 
and  in  a  reguline  state;  second,  it  should  not  decompose,  or 
deposit  its  dissolved  metal,  by  contact  with  the  atmosphere, 
or  by  exposure  to  light ;  third,  it  should  not  act  chemically 
to  any  great  extent,  upon  the  base  metals,  or  upon  those  to 
be  coated ;  fourth,  it  should  dissolve  the  anode  sufficiently 
freely ;  fifth,  it  should  possess  good  electrical  conducting 


Testing  a  Depositing  Liquid.  341 

power  j  sixth,  it  should  not  evolve  gas  at  the  surface  of  the 
articles.  The  three  first  conditions  are,  I  consider,  indispens- 
able, and  if  it  fail  in  either,  it  is  worthless  or  nearly  so,  for  the 
purposes  of  electro-deposition. 

Testing  a  depositing  liquid. — From  what  has  just  been  said, 
the  mode  of  testing  is  obvious.  To  test  it,  pass  a  current 
from  two  or  three  Smee's  cells  through  it,  by  clean  and 
weighed  anodes  and  cathodes,  the  latter  being  composed  of 
the  particular  metal  which  it  is  intended  to  coat.  Observe 
the  quality  of  the  deposit,  the  speed  of  deposition,  and 
whether  much  gas  is  evolved  from  the  electrodes.  Set  a 
portion  of  the  clear  liquid  aside,  in  a  colourless  glass  vessel, 
exposed  to  light  and  air,  and  observe  if  it  acquires  a  film, 
deposits  a  sediment,  changes  in  colour,  evolves  gas,  or 
shows  any  other  signs  of  decomposition.  Immerse  in  a 
separate  portion,  for  about  a  quarter  of  an  hour  (that  will 
be  abundance  of  time),  a  bright  and  perfectly  clean  piece  of 
metal,  of  the  kind  to  be  deposited,  and  observe  if  it  becomes 
coated  with  the  dissolved  metal,  or  changes  in  appearance 
in  any  way.  A  liquid  which  requires  a  strong  current  to 
make  it  yield  its  metal  freely,  or  which  liberates  gas  at  the 
cathode,  but  has  no  other  defects,  does  no  harm  except  being 
wasteful  of  the  electric  power.  One  which  evolves  gas 
at  the  anode,  becomes  gradually  deprived  of  its  dissolved 
metal. 

Practical  management  of  depositing  solutions  (see  also  p. 
QOt/jqgr.)* — Having  obtained  a  good  depositing  liquid,  we 
must  manage  to  keep  it  so  ;  because  a  large  vat  of  silver  solu- 
tion, or  a  vessel  of  gilding  liquid,  is  valuable.  The  operator 
should  as  far  as  possible,  avoid  doing  anything  to  such 
liquids  which  will  alter  their  chemical  composition  ;  many 
valuable  ones  have  been  injured  and  spoiled,  by  persons 
(unused  to  making  careful  experiments)  adding  substances 
to  them,  with  the  hope  of  improving  them.  The  tales  told 
by  electro-platers  of  their  experiences  with  depositors,  in 
making  and  mending  electro-plating  solutions,  should  act  as 


3  42  The  A  rt  of  Electro- Metallurgy. 

warnings  to  those  about  to  commence  in  the  art  upon  a 
large  scale.  One  discovered  that  the  operator,  by  using 
cyanide  of  potassium,  regardless  of  its  strength,  to  make 
cyanide  of  silver,  re-dissolved  about  sixty  ounces  of  silver, 
and  threw  it  away  in  the  wash- waters.  Another  had  a  similar 
mishap  with  eleven  ounces  of  gold.  A  third  had  450  ounces 
of  silver  converted  into  waste  residue.  A  fourth  had  two 
large  vats  of  silver  solution  rendered  incurable,  by  addition 
of  too  much  '  brightening '  liquid ;  and  many  electro-platers 
have  had  similar  mishaps.  Others  have  found  their  anodes 
dissolve  with  extraordinary  rapidity,  through  the  use  of  too 
much  free  cyanide,  or  by  allowing  them  to  remain  in  contact 
with  the  iron  vat,  and  have  been  surprised  to  find,  that  a 
solution,  which  when  made,  contained  only  an  ounce  of 
silver  per  gallon,  held  in  solution  more  than  four  times  as 
much.  Others,  by  keeping  a  record  of  the  silver  dissolved 
and  deposited,  as  well  as  of  that  found  in  the  liquid  by  an- 
alysis, have  missed  a  considerable  quantity,  and  ultimately 
found  that  it  had  soaked  into  the  sides  of  the  thick  wooden 
vats.  The  composition  of  a  depositing  solution  should  not 
be  altered,  except  so  far  as  it  can  be  done  with  perfect  safety, 
as  by  diluting  it  to  a  certain  extent  with  water,  or  adding 
materials  to  exactly  re-place  those  abstracted  from  it.  The 
electric  power  should  always  be  adapted  to  the  liquid,  and 
not  the  latter  to  the  electric  power.  The  electrodes  should 
as  a  rule,  be  kept  nearly  equal  in  amount  of  surface,  the 
anode  being  in  some  cases  the  largest ;  and  the  quality  of 
the  deposit  should  not  usually  be  regulated  by  altering  their 
proportionate  extent  of  surface,  but  by  altering  the  battery 
or  other  source  of  the  current. 

As  a  general  rule,  in  order  to  prevent  depositing  liquids 
gradually  becoming  contaminated  with  foreign  metals,  any 
metal  which  will  be  corroded  by  a  particular  depositing 
liquid  (and  which  will  therefore  coat  itself  by  simple  im- 
mersion in  that  liquid),  should  previously  receive  a  coating 


Propers-Position  of  Objects  dztring  Deposition.    343 

of  suitable  metal  in  a  preparing  solution ;  for  instance,  iron 
articles  which  are  to  receive  a  thick  coating  of  copper,  are 
first  coated  with  a  thin  film  of  that  metal  in  a  cyanide 
liquid. 

Anodes  of  any  metal  may  be  formed  of  scraps,  but  that 
is  not  advisable,  if  better  ones  can  be  obtained. 

Proper  position  of  articles  and  dissolving  plates  in  the 
vats. — Both  the  articles  and  the  plates  should  be  wholly  sub- 
merged in  the  liquid ;  the  former  being  a  little  the  deepest. 
Both  should  be  vertical,  or  nearly  so ;  the  plates  may  however 
overhang  a  little  with  advantage :  it  makes  them  dissolve 
more  evenly.  The  horizontal  position,  with  the  dissolving 
metal  above,  although  the  most  scientifically  correct  ar- 
rangement, does  not  succeed  in  practical  working,  because 
the  metal  used  for  dissolving  is  never  quite  pure  (with  nickel 
and  copper  especially),  and  the  impurities  from  it,  fall  upon 
the  surface  of  the  receiving  article  beneath,  and  make  it 
rough ;  in  addition  to  this,  the  position  of  the  article  pre- 
vents its  being  easily  removed  or  examined.  If  the  object 
to  be  coated,  has  a  very  irregular  outline,  either  the  dis- 
solving plate  should  be  bent  somewhat  to  its  form,  so  that 
the  two  may  be  nearly  equidistant  at  all  parts ;  or  the  article 
should  be  often  shifted  in  its  position,  so  as  to  produce  a 
nearly  uniform  thickness  of  coating  all  over.  The  nearer 
the  receiving  surface  is  to  the  dissolving  plate,  the  more  rapid 
is  the  deposition,  and  a  large  body  of  liquid,  deposits  more 
rapidly  and  more  evenly  than  a  small  one.  The  greatest 
thickness  of  coating  always  takes  place  upon  the  most 
prominent  places,  i.e.,  upon  those  parts  nearest  the  dis- 
solving metal.  If  it  is  desired  to  prevent  vertical  lines  in 
a  thick  deposit,  the  object  must  be  kept  in  motion; — the 
means  of  doing  this  has  been  already  described  (see  .pp. 
171-174). 

Motion  of  the  articles  is  very  advantageous :  it  permits 
much  more  rapid  deposition  ;  it  keeps  the  solution  much 


344  The  A  rt  of  Electro-Metallurgy. 

more  uniform  in  composition,  prevents  the  lower  portions 
of  the  objects  being  coated  so  much  faster  than  their  upper 
ones,  and  also  prevents  the  upper  parts  of  the  anodes  being 
dissolved  so  much  more  rapidly  than  their  lower  ones.  In 
addition  to  this,  by  keeping  the  solution  mixed,  it  greatly 
diminishes  the  electric  conduction  resistance,  which  would 
be  produced  by  polarisation,  due  to  layers  of  liquid  of  oppo- 
site electrical  nature,  collecting  in  contact  with  the  electrodes 
(see  p.  54). 

As  most  of  the  deposit  takes  place  upon  the  parts  of  the 
article  nearest  the  dissolving  plate,  if  other  parts  require 
also  a  thick  deposit,  the  article  must  be  so  placed,  or  an 
anode  must  be  employed  of  such  a  shape,  as  to  effect  that 
object. 

Regulation  of  the  deposit. — Regulation  of  the  quality  of 
the  deposited  metal  is  always  an  important  matter,  and  with 
all  metals,  except  a  very  limited  number,  it  is  one  of  the  most 
difficult  objects  to  effect.  As  a  general  rule,  the  greater  the 
electro-motive  force,  and  the  smaller  the  quantity  of  the 
current,  the  harder  and  brighter  is  the  deposited  metal ;  but 
this  of  course  only  holds  good  in  the  case  of  a  liquid  which 
is  capable  of  yielding  such  metal.  The  chief  points  are,  first 
to  obtain  a  good  liquid,  at  the  proper  temperature,  and  second 
to  adjust  the  density  of  the  current  (see  p.  38)  until  the  re- 
quired kind  of  deposit  is  obtained.  Some  liquids  are  so 
constituted,  (especially  those  of  the  more  easily  oxidizable 
base  metals,  such  as  manganese,)  that  if  the  current  is  only  of 
sufficient  density  to  deposit  it  in  a  bright  reguline  state,  it  is 
not  sufficiently  dense  to  prevent  the  metal  at  once  taking  up 
oxygen  and  forming  a  sub-oxide.  If,  in  a  good  depositing 
solution  of  a  non-readily  oxidizable  metal,  such  as  copper, 
we  are  producing  by  means  of  a  current  of  considerable 
electro-motive  force,  a  black  powder  deposit,  upon  a  very 
small  article,  a  much  larger  article  would  receive  by  the  same 
current  a  reguline  deposit,  and  upon  a  very  much  larger 
one  the  deposit  would  be  hard  and  crystalline.  So  much, 


Regulation  of  the  Deposition.  345 

however,  depends  in  every  case  upon  the  special  charac- 
teristics of  the  particular  liquid,  that  these  can  only  be  con- 
sidered as  general  instructions  for  the  guidance  of  the  electro- 
depositor.  This  part  of  the  subject  has  also  been  already 
treated  of  in  previous  parts  of  this  book  (see  pp.  35-39,  54-55, 
and  90-93)- 

The  action  of  a  current  of  great  electro-motive  power, 
but  small  in  quantity,  appears  in  some  cases  (for  instance 
with  copper),  to  confer  upon  the  deposited  particles,  a  kind  of 
polarity,  a  power  of  grouping  themselves  into  separate  warty 
nodules  or  groups  of  crystals,  each  of  which,  as  it  becomes 
larger,  appears  to  powerfully  repel  all  particles  in  its  neigh- 
bourhood, and  thus  causes  the  metal  to  spread  rapidly ;  when 
this  action  is  continued  to  a  considerable  thickness  of  deposit, 
especially  in  cold  weather,  the  metal  is  exceedingly  hard,  and 
easily  broken  into  a  number  of  distinct  grains  or  nodules,  which 
are  in  the  form  of  lumps  with  rounded  edges.  With  a  current 
from  100  pairs  of  Smee's  battery,  acting  for  a  long  period  of 
time  in  cold  weather,  and  the  quantity  of  the  current  kept 
down  to  the  lowest  possible  degree,  I  have  seen  a  tough 
deposit  of  zinc  spread  over  several  square  inches  of  clean 
gutta-percha;  and  in  depositing  copper  by  a  current  of 
rather  high  intensity,  and  small  quantity,  upon  black-leaded 
gutta-percha  medallions,  I  have  repeatedly  observed,  that 
where  there  was  a  sunken  boundary  line  near  the  edge,  the 
deposit  remained  quite  thin,  as  if  powerfully  repelled,  whilst 
on  each  side  of  the  line  it  was  very  thick,  and  on  the  outside 
edge  accumulated  in  large  masses,  hard  and  distinctly 
separate,  and  containing  as  much  metal  as  the  whole  of  the 
medallion  besides.  The  effect  of  lines  is  often  seen  in 
electro-copies  of  set-up  type,  and  the  deposits  are  very  fragile 
at  those  parts. 

With  regard  to  the  regulation  of  the  quantity  of  the  de- 
posited metal,  that  part  of  the  subject  has  been  treated  of  in 
the  theoretical  division  (see  pp.39-44,  74-75).  We  know  that 
when  all  the  arrangements,  are  properly  made  and  carried 


346  The  A  rt  of  Electro-Metallurgy. 

out,  the  quantity  of  metal  dissolved  and  deposited  in  the 
vat,  is  in  direct  proportion  to  the  quantity  of  zinc  dissolved, 
and  acid  consumed,  in  each  alternation  of  the  battery.  With 
a  perfect  depositing  liquid,  good  battery  arrangements,  and 
pure  materials,  for  every  equivalent  of  zinc,  dissolved  in  each 
alternation  of  the  battery,  an  equivalent  of  metal  is  dissolved 
on  one  side,  and  an  equivalent  deposited  on  the  other,  in 
the  depositing  vessel.  For  instance,  for  every  equivalent 

f  -!  =  32-5  parts )  of  zinc  so  dissolved,  and  5-  =49  parts, 

\2  J  2 

or  one  equivalent,  of  oil  of  vitriol  consumed  in  the  battery, 
an  equivalent  (  -— -  =  3175  parts  J  of  copper  is  deposited 

in  the  sulphate  of  copper  solution,  or  an  equivalent  (108 
parts)  of  silver  in  the  cyanide  of  silver  plating  liquid,  and  a 
similar  quantity  of  copper  or  silver  dissolved  at  the  anode. 
But  in  practical  working,  the  materials  are  rarely  if  ever 
pure,  or  the  arrangements  perfect ;  the  zinc  nearly  always 
contains  a  small  proportion  of  other  substances,  the  mercury 
contains  tin  or  lead,  and  the  sulphuric  acid  contains  a  little 
nitric  acid,  or  plumbic  sulphate.  The  acid  liquid  of  the 
battery  is  often  too  strong ;  much  of  it  is  also  thrown  away 
before  it  is  completely  exhausted.  The  zinc  plates  are 
not  kept  well  amalgamated,  or  the  silver  well  platinized,  or 
the  plates  are  suffered  to  remain  too  long  in  the  liquid  when 
not  in  use.  The  metal  of  the  anode  is  also  frequently  impure  ; 
occasionally  some  of  the  deposit  is  allowed  to  re-dissolve, 
from  the  battery  power  becoming  low,  and  from  not  stirring 
the  solution  ;  in  some  solutions,  a  part  of  the  electric  current 
is  expended  in  evolving  gas  at  the  cathode ;  and  finally,  the 
repeated  operation  of  *  scratching,'  removes  some  of  the 
deposit.  Allowing  for  all  these,  and  other  unavoidable 
sources  of  loss,  in  practical  working,  about  one  pound  only 
of  copper,  can  be  deposited  in  the  ordinary  sulphate  solu- 
tion, by  the  consumption  of  from  one  and  a  quarter  to  one 


Magneto- Electric  Machines.  347 

and  a  half  pounds  of  zinc,  and  an  equivalent  quantity  of 
acid,  in  each  alternation  of  the  battery. 

With  regard  to  regulation  of  the  speed  of  deposition,  (see 
p.  337)  •  with  every  liquid  there  is  a  limit  of  rate  of  deposition 
per  given  amount  of  surface,  beyond  which  it  is  impossible 
to  obtain  good  metal  (see  p.  38),  and  that  limit  differs  with 
every  different  liquid,  and  probably  with  each  liquid  at  every 
different  temperature,  besides  being  dependent  upon  the 
kind  of  receiving  surface.  It  is  well  known  to  electro-depo- 
sitors, that  it  is  usually  much  more  difficult  to  produce  a 
reguline  deposit  upon  rough  surfaces,  than  upon  smooth 
ones  ;  upon  cast-iron  than  upon  most  other  metals,  and  that 
to  obtain  it  at  all  upon  that  metal,  the  rate  of  deposit 
must  be  less,  than  upon  a  smooth  surface  of  pure  copper 
or  silver. 

Magneto -electric  machines. — The  fundamental  principle  of 
all  magneto-electric  machines,  has  been  already  stated  and 
illustrated  (see  p.  57).  As  this  is  not  a  treatise  upon 
dynamic  electricity,  but  only  upon  the  applications  of  it  to 
metallurgical  operations,  and  as  the  spa^e  at  my  command 
is  only  limited,  and  a  clear  and  full  description  of  magneto- 
electric  machines  would  occupy  too  much  space,  I  am 
only  enabled  to  insert  a  very  brief  statement  respecting  these 
electro-motors. 

Figures  52  and  53  represent  Wilde's  magneto-electric 
machine.  It  consists  essentially  of  two  electro-magnets, 
a  small  and  a  large  one,  with  insulated  copper  wire  coiled 
transversely  upon  them;  and  with  armatures  of  soft  iron 
(see  fig.  53)  (also  with  insulated  copper  wire  coiled  length- 
wise upon  them),  revolving  between  their  poles.  The  residual 
magnetism  of  the  small  (or  upper)  electro-magnet,  excites  a 
feeble  current  in  the  coil  of  its  revolving  armature.  This 
current  circulates  through  the  wires  of  both  the  magnets, 
and  increases  the  magnetism  ;  and  the  increased  magnetism 
of  the  small  one,  reacts  upon  the  armature,  and  increases  the 


343  The  A  rt  of  Electro-Metallurgy. 


Magneto-Electric  Machines.  349 

current,  and  so  on,  until  both  the  magnets  are  saturated  with 
magnetism  at  the  expense  of  mechanical  power.  The  cur- 
rent from  the  revolving  armature  of  the  large  one  alone,  is 
used  for  electro-deposition,  or  other  purposes.  '  The  arma- 
tures of  both  machines  are  driven  at  a  speed  of  about  2,000 
revolutions  per  minute,  and  at  this  rate,  the  current  from 
the  large  one,  deposits  twenty-eight  ounces  of  silver  an  hour, 
with  an  expenditure  of  two  horse  power.' 

These  machines  are  in  extensive  use  at  the  works  of 
Messrs.  Elkington  and  Co.,  in  Birmingham,  for  the  purposes 
of  depositing  copper  statues,  and  for  general  plating  with 
silver ;  also  at  the  copper  works  of  the  same  company  at 
Pembrey,  near  Swansea  ;  for  purifying  by  electrolysis  upon 
the  large  scale,  crude  slabs  of  unrefined  copper  from  the 
ordinary  smelting  process.  A  single  '  multiple  armature'  ma- 
chine of  Wilde's  (see  '  Philosophical  Magazine,'  June  1873), 
at  those  works,  deposits  four  and  a  half  hundredweights  of 
copper  in  twenty-four  hours.  These  machines  have  also 
been  successfully  applied  to  the  economic  production  of 
coppered  iron  rollers  for  calico-printing.  To  keep  the  arma- 
ture cool,  the  ends  of  the  large  electro-magnet  are  made 
hollow,  and  a  current  of  cold  water  caused  to  flow  through 
the  cavities. 

Gramme's  magneto-electric  machine  is  shown  in  fig.  54. 
It  consists  essentially  of  a  ring  of  soft  iron,  covered  with  a 
large  number  of  coils  of  insulated  copper  wire,  the  respec- 
tive ends  'of  which  are  connected  with  the  separate  sections 
of  two  commutators  fixed  upon  the  axis  of  the  machine. 
The  ring  with  its  coils  and  commutators,  fixed  upon  the  axis, 
revolves  between  the  poles  of  an  electro-magnet. 

By  this  machine — '  To  deposit  600  grammes  of  silver 
requires  one  horse  power,  and  a  speed  of  300  turns  per 
minute  ;  the  tension  of  the  current  being  equal  to  that  of  two 
Bunsen's  cells,  and  its  quantity  equal  to  thirty-two  such  cells 
of  ordinary  size.  At  a  speed  of  275  revolutions  per  minute, 
it  has  deposited  525  grammes  of  silver  per  hour;  at  300 


350  The  A  rt  of  Electro-Metallurgy. 

turns,  605  grammes  ;  and  at  325  turns,  675  grammes.     The 
weight  of  the  copper  wire  on  the  fixed  electro-magnets  was 

FIG.  54- 


135,  and  on  the  moveable  ones  forty  kilogrammes'  ('Tele- 
graphic Journal,'  vol.  i.  p.  54).  '  The  present  form  of  the 
machine  as  used  for  electro-deposition  is  composed  as 
follows  : — 

Total  weight          .         .         .         .  H7'5    kilogrammes 

Copper  coils 47 '°  » 

Total  height '6    metre 

Total  width '55     » 

Deposits  silver  per  hour          .         .  600  •      grammes 
Required  power  to  work  it      .         •       5°'      kilogrammetres.' 

(<  Telegraphic  Journal,'  vol.  iii.  p.  198).     This  machine  is  in 


Thermo- Electric  Piles.  351 

use  at  Messrs.  Christople's  large  electro-plating  works  in 
Paris. 

The  most  recent  form  of  magneto- electric  machine,  is 
that  of  Messrs  Siemens  and  Alteneck,  a  description  of  which, 
with  engravings  of  it,  may  be  found  in  the  '  Electrical  News,' 
vol.  i.  p.  226. 

The  chief  obstacle  hitherto  met  with  in  the  use  of  these 
machines  has  been,  that  after  a  few  hours'  action,  the  different 
parts  are  liable  to  become  considerably  heated,  partly  by  the 
incessant  molecular  changes  attending  the  variations  of  mag- 
netism, and  partly  by  the  conduction  resistance  in  the  coils 
of  wire.  This  has  been  largely  overcome  in  Mr.  Wilde's 
machine  by  the  employment  of  several  small  machines  in- 
stead of  one  large  one,  and  by  allowing  a  stream  of  cold  water 
to  run  through  the  hollow  ends  of  the  magnet.  In  Gramme's 
machine,  provided  it  is  not  worked  too  fast,  the  heat  is  re- 
duced to  a  moderate  amount;  and  in  a  large  machine  of 
Siemens  and  Alteneck's  in  the  Vienna  Exhibition,  I  also 
observed  but  little  rise  of  temperature,  after  it  had  been  in 
action  a  considerable  time.  Another  objection  to  some  of 
these  machines,  is  the  complexity  of  the  commutator.  The 
electric  current  from  all  these  magnetic  machines,  is  regulated 
for  electro-metallurgical  purposes,  by  interposing  a  piece  of 
thin  iron-wire  in  the  circuit. 

Thermo-electric  piles. — The  two  most  efficient  kinds  of 
this  instrument,  appear  to  be  those  of  Noe  of  Vienna,  and 
Clamond  of  Paris.  The  former  is  the  more  quickly  excited, 
and  gives  a  powerful  current;  and  the  latter  is  the  most 
strongly  constructed. 

Noe's  pile  (see  fig.  55)  consists  of  small  cylinders,  about 
one  and  a  quarter  inches  long,  and  three  eighths  of  an  inch 
diameter,  of  an  alloy  of  about  thirty-six  and  a  half  parts  of 
zinc,  and  sixty-two  and  a  half  of  antimony  as  the  positive, 
and  stout  German-silver  wire  as  the  negative  element. 
Twelve  of  these  pairs  have  an  electro-motive  force  of  one 
DanielPs  cellt  and  twenty  of  them  that  of  one  Bunsen.  The 


352 


The  Art  of  Electro-Metallurgy. 


resistance  of  twenty  of  them  is  about  equal  to  one  ohm  (see 
pp.  70-73).  With  a  great  external  resistance,  twenty  of 
them  are  equal  to  one  Bunsen's,  and  with  a  small  external 
resistance,  twenty  quadrupled  ones  are  somewhat  stronger 
than  one  of  Bunsen's  elements  (Watts'  *  Chemical  Dictionary,' 
supplement,  p.  458.  Wiedemann's  'Galvanismus  und  Elek- 
tromagnetismus,'  1872,  vol.  i.  p,  824.  'Journal  of  the  Chemi- 
cal Society,'  vol.  ix.  p.  989,  vol.  xi.  p.  465). 

The  construction  of  a  few  elements,  is  shown  in  the 
annexed  figure.  The  junctions  of  the  elements  are  heated 
by  small  gas-rlames,  and  the  alternate  junctions  are  cooled 


FIG.  55- 


Cu 


by  the  heat  being  conducted  away  by  large  blackened  sheets 
of  thin  copper.  To  protect  the  German-silver  wire  from 
oxidation,  it  is  enclosed  in  a  tube  of  that  alloy  where  the 
flame  impinges  against  it  ;  and  to  prevent  the  ends  of  the 
positive  cylinders  being  melted,  they  are  faced  with  iron 
and  a  thin  sheet  of  mica.  The  German-silver  wire  may  be 
heated  to  low  redness.  The  usual  form  of  the  apparatus  is 
in  ninety-six  elements,  which  may  be  either  used  as  ninety- 
six  by  one,  forty-eight  by  two,  or  twenty-four  by  four ;  an  1 
instantly  changed  from  one  to  the  other  of  these  arrangements, 


Thermo-Electric  Piles. 


353 


by  means  of  a  most  ingenious  and  effective  current  trans- 
poser,  which  does  not  require  cleaning.  The  current 
attains  its  maximum  strength  in  about  one  minute  ;  that 
from  the  single  series  decomposes  water  rapidly ;  and  that 
from  the  quadruple  series  excites  a  large  electro-magnet 
powerfully.  I  have  used  this  apparatus  with  great  satisfac- 
tion for  many  brief  experiments.  The  instrument  is  made 
by  W.  J.  Hauck,  Kettenbriickengasse  20,  Vienna  ;  also  by 
P.  Dorfell,  Berlin.  It  is,  I  am  informed,  in  use  for  electro- 
plating in  Dittmar's  electrotype  and  lamp  manufactory, 
Vienna. 

FIG.  56. 


Fig.    56   represents  a  small  Clamond's  pile,  connected 
for  intensity  (see  also  'Telegraphic  Journal/  vol.  i.  p.  12). 

A  A 


354  Tke  A  rt  of  Electro- Metallurgy. 

The  elements  are  tinned  sheet-iron  as  negative,  and  an  alloy 
of  two  parts  of  zinc  and  one  part  of  antimony  as  positive. 
A  pile  which  consumes  150  litres  of  gas  per  hour,  is  capable 
of  depositing  one  kilogramme  of  copper,  at  a  cost  of  two 
francs  fifty  centimes  (*  Telegraphic  Journal/  vol.  iii.  pp.  157 
and  319).  According  to  the  inventors,  *  a  machine  of  100 
bars,  with  a  consumption  of  8  to  9  cubic  feet  of  gas,  deposits 
about  an  ounce  of  silver  per  hour.  The  same  apparatus 
coupled  for  quantity,  will  deposit  about  one  ounce  of  copper 
in  the  same  time,'  '  100  bars,  coupled  for  quantity,  have 
an  electro-motive  force  of  about  five  volts,  and  an  internal 
resistance  of  one  ohm'  (see  pp.  70-75).  Clamond's  pile  is 
being  used  for  electro-plating  and  depositing,  in  various 
establishments  in  Birmingham,  London,  Sheffield,  and  other 
places.  Its  durability  is  being  improved. 

SPECIAL   INFORMATION   RESPECTING   SUBSTANCES   USED 
IN   THE   ART. 

As  there  are  various  substances  used  in  the  different  pro- 
cesses of  electro-deposition,  it  will  be  useful  to  the  practical 
operator  in  the  art,  to  be  acquainted  with  some  special 
technical  points  of  information  respecting  them,  which  may 
affect  the  success  of  his  operations,  and  which  have  not 
already  been  given  in  the  body  of  the  book. 

Water. — Distilled  water  is  the  most  suitable  for  making 
solutions.  It  should  give  no  cloud,  on  adding  to  separate 
portions  of  it,  a  few  drops  of  solutions  of  argentic  nitrate, 
chloride  of  barium,  or  oxalate  of  ammonium  ;  nor  become 
brown  on  addition  of  sulphuretted  hydrogen  water.  If  dis- 
tilled water  cannot  be  conveniently  obtained,  filtered  rain- 
water may  usually  be  employed  in  its  stead. 

Nitric  add. — Called  also  aqua  fortis.  The  pure  acid  for 
dissolving  silver,  &c.,  should  be  colourless,  have  a  specific 
gravity  of  not  less  than  1*52  ;  and  separate  portions  of  it, 
diluted  with  pure  distilled  water,  should  give  no  cloud  with 


Substances  tised  in  the  A  rt.  355 

a  single  drop  of  solution  of  nitrate  of  silver,  or  of  chloride  of 
barium.  It  should  be  kept  in  a  stoppered  bottle,  in  a  dark, 
cool,  and  dry  place.  If  a  drop  of  this  or  any  other  acid  falls 
upon  one's  clothes,  diluted  aqueous  ammonia  should  at  once 
be  freely  applied. 

All  the  pure  strong  acids  should  be  kept  in  stoppered 
bottles,  in  a  dry  place.  Carboys  of  common  acids,  and  dipping 
liquids,  should  have  stoneware  stoppers,  and  be  kept  in  an 
outhouse. 

Hydrofluoric  add. — Called  also  fluoric  acid.  This  liquid  is 
always  very  impure.  It  should  be  kept  in  a  bottle  of  gutta- 
percha,  provided  with  a  stopper  of  india-rubber,  in  a  dry  and 
cool  place,  and  not  in  close  proximity  to  glass  vessels, 
because  the  vapour  corrodes  them.  It  is  highly  dangerous 
to  breathe  the  fumes  of  this  acid ;  and  if  a  drop  of  it  falls 
upon  the  skin  it  should  be  thoroughly  washed  off  at  once, 
otherwise  after  a  few  hours  great  pain  will  be  suffered. 

Hydrochloric  acid. — Called  also  '  muriatic  acid,'  '  spirits  of 
salt,'  and  '  smoking  salts.'  The  pure  acid  should  be  colour- 
less, of  not  less  specific  gravity  than  1*20.  It  should  be 
kept  in  a  cool  place. 

Aqua  regia. — Called  also  nitro-hydrochloric  acid.  This 
is  a  mixture  of  one  volume  of  nitric,  and  from  two  to  three 
of  hydrochloric  acid.  It  should  not  be  prepared  until 
required  to  be  used,  because  it  decomposes  spontaneously. 

Blacklead. — Called  also  plumbago  and  graphite.  This 
substance  always  contains  a  little  earthy  matter,  silica, 
oxide  of  iron,  &c.  The  most  suitable  kind  is  usually  very 
black,  but  without  much  lustre,  until  after  rubbing.  It  should 
adhere  to  the  articles,  and  not  become  detached  when  they 
are  immersed  in  the  solutions.  The  best  can  only  be  selected 
by  means  of  actual  trial,  and  should  be  gilded  or  silvered  (see 
p.  217). 

Sulphuretted  hydrogen. — Called  also  hydric- sulphide,  sul- 
phide of  hydrogen,  &c.  This  substance  is  a  gas,  and  may 
easily  be  prepared  by  putting  some  fragments  of  prepared 

A  A  2 


356  The  A  rt  of  Electro-  Metallurgy. 

sulphide  1  of  iron  ('  sulphuret  of  iron  '),  into  a  flask  with  some 
water,  and  then  adding  sulphuric  acid.  The  gas  should  be 
washed  by  passing  it  through  a  small  quantity  of  water.  Sul- 
phuretted hydrogen  water  is  prepared  by  passing  the  washed 
gas  in  bubbles  through  distilled  water  until  the  water  is 
saturated.  The  water  dissolves  only  about  three  times  its 
bulk  of  the  gas  ;  or  one  part  by  weight  of  the  gas  dissolves 
in  about  250  parts  of  water.  The  solution  soon  decom- 
poses. 

Sulphurous  anhydride.  —  Called  also  '  sulphurous  acid.' 
This  is  best  prepared,  by  heating  in  a  glass  flask,  strong  oil 
of  vitriol,  containing  fragments  of  copper  wire.  The  flask 
should  be  protected  from  direct  contact  with  the  flame  by  a 
sheet  of  iron  wire  gauze. 

Sulphuric  add.  —  Called  also  '  oil  of  vitriol.'  The  pure 
acid  should  have  a  specific  gravity  of  not  less  than  1-85,  and 
be  nearly  or  quite  colourless.  The  least  trace  of  dust  or 
organic  matter,  imparts  a  darkness  of  appearance  to  it.  It 
should  be  kept  in  a  dry  place.  When  diluting  it,  the  water 
should  not  be  poured  into  the  acid,  because  that  is  dangerous, 
but  the  acid  into  the  water,  and  that  slowly  (see  also  p. 


^ 

Bisulphide  of  carbon.  —  Called  also  'sulphuret  of  carbon/ 
and  '  carbon  disulphide.'  This  is  a  very  volatile  and  inflam- 
mable liquid,  and  a  flame  should  not  therefore  be  brought 
near  its  vapour.  It  should  be  kept  in  a  well-stoppered  or 
corked  bottle,  in  a  cool  place. 

Phosphorus.  —  This  substance  should  be  kept  in  a  wide- 
mouthed  stoppered  bottle,  filled  with  water,  to  keep  the  air 
from  contact  with  it.  The  bottle  should  also  be  covered 
with  black  varnish,  and  kept  in  a  dark  place,  because  the 
light  changes  the  phosphorus  and  makes  it  insoluble.  Phos- 
phorus should  never  be  exposed  to  the  air  for  more  than  a 
few  seconds,  or  it  may  inflame  ;  and  it  should  always  be 
cut  whilst  under  the  surface  of  water. 

1  Containing  one  equivalent  of  sulphur  to  one  of  iron. 


Substances  used  in  the  Art.  357 

Phosphorus  solution. — Called  also  *  Greek  fire/  This 
highly  inflammable  and  dangerous  mixture,  composed  of 
phosphorus  dissolved  in  bisulphide  of  carbon,  has  been 
already  described  (see  p.  218).  It  should  only  be  prepared 
in  small  quantity ;  and  the  bottle  containing  it  should  be 
kept  in  a  cool  place,  partly  immersed  in  sand,  in  a  stoneware 
vessel  covered  with  a  metal  lid.  It  is  extremely  liable  to 
spontaneous  combustion,  especially  if  any  be  spilt. 

Arsenious  acid. — Commonly  called  '  white  arsenic.'  Only 
a  small  quantity  of  this  is  required.  The  bottle  containing 
it  should  be  kept  in  a  dry  place,  out  of  the  reach  of  careless 
persons,  and  should  be  distinctly  labelled  '  poison.' 

Antimony. — In  purchasing  this  metal,  what  is  known  as 
the  '  best  star  antimony '  should  be  selected.  It  may  be 
known  by  its  whiter  appearance,  and  by  having  crystalline 
markings,  looking  like  fern-leaves,  upon  its  surface. 

Bismuth. — This  metal  varies  a  little  in  quality,  and  is 
liable  to  contain  traces  of  arsenic,  and  sometimes  also  of 
copper.  The  purer  kinds  are  very  much  higher  in  price  than 
the  common  variety. 

Chloride  of  platinum. — Called  also  '  platinic  chloride,' 
'  muriate  of  platinum,'  &c.  As  the  substance  sold  in  shops 
is  liable  to  contain  a  variable  proportion  of  platinum,  it  is 
best  for  the  operator  to  prepare  the  salt  himself,  according  to 
the  directions  already  given  (see  p.  118). 

Chloride  of  gold. — Called  also  *  muriate  of  gold,'  and 
'  auric  chloride.'  It  is  better  to  prepare  this  than  to  purchase 
it,  because  the  commercial  article  is  liable  to  contain  a 
variable  proportion  of  gold;  it  should  contain  65-2  percent, 
of  that  metal  (see  p.  122). 

Silver. — This  metal  may  be  tested  for  copper,  by  dis- 
solving it  in  warm  dilute  nitric  acid,  precipitating  all  the 
silver  by  means  of  a  slight  excess  of  hydrochloric  acid,  and 
then  adding  a  drop  of  solution  of  ferrocyanide  of  potassium, 
or  by  adding  ammonia  to  the  solution  of  argentic  nitrate, 
until  all  the  precipitate  first  formed  is  re-dissolved.  Now  look 


3  5  8  The  A  rt  of  Electro-  Metallurgy. 

down  through  a  considerable  depth  of  the  clear  liquid ;  if  a 
blueness  is  visible,  copper  is  present 

Nitrate  of 'silver.— -Called  also  'argentic  nitrate/  'lunar 
caustic/  &c.  It  should  be  in  colourless  crystals,  free  from 
odour  of  nitric  acid,  entirely  soluble  in  distilled  water,  and 
should  contain  63^  per  cent,  of  silver.  To  ascertain  the  latter 
point,  simply  melt  it  at  a  full  red  heat,  with  a  little  borax  in 
an  earthen  crucible,  and  weigh  the  metal ;  or  precipitate  its 
solution  by  a  slight  excess  of  dilute  hydrochloric  acid,  wash, 
dry,  and  weigh  the  precipitate;  143^  parts  of  it  equal  108  of 
silver. 

Chloride  of  silver. — Called  also  '  argentic  chloride/  '  horn- 
silver/  and  '  muriate  of  silver.'  This  substance  should  con- 
tain 75!  per  cent,  of  silver.  To  ascertain  its  percentage, 
melt  it,  at  a  full  red  heat,  with  an  excess  of  perfectly  dry 
(i.e.  anhydrous)  carbonate  of  sodium,  in  an  earthen  crucible, 
and  weigh  the  button  of  silver.  The  chloride  is  decomposed 
by  light,  and  should  be  kept  in  an  opaque  bottle  in  a  dark 
place. 

Mercury. — Called  also  'quicksilver.'  Pure  mercury  is 
perfectly  bright,  and  leaves  no  tail  of  drossy  appearance,  on 
pouring  it  all  slowly  out  of  a  vessel :  it  also  volatilises  entirely 
by  heat.  It  should  be  kept  in  strong  bottles,  and  not  allowed 
to  come  into  contact  with  any  metals,  except  iron,  platinum, 
or  aluminium. 

Amalgam  of  gold. — To  prepare  it,  heat  pure  mercury  to 
about  200°  G,  and  add  to  it  the  gold  in  foil  or  ribbon  ;  the 
gold  is  readily  absorbed  and  forms  the  amalgam. 

Sulphate  of  copper. — Called  also  cupric  sulphate,  '  blue 
vitriol/  '  blue-stone/  '  Roman-vitriol/  &c.  The  pure  salt 
should  be  in  large  crystals  of  a  deep  blue  colour,  without 
any  admixture  of  green  ;  the  latter  indicates  the  presence  of 
iron.  To  test  for  iron,  dissolve  a  little  of  the  salt  in  distilled 
water,  add  aqueous  ammonia  with  stirring,  until  all  the  blue 
precipitate  is  re-dissolved.  After  standing  some  time,  pour 
away  the  clear  blue  liquid,  add  distilled  water  freely  to  the 


Substances  used  in  the  Art.  359 

residue,  and  allow  it  to  stand  for  some  time  again  ;  a  residue 
of  red  brown  powder,  indicates  the  presence  of  iron. 

Nickel — This  metal  is  always  contaminated  with  silicon 
and  carbon,  which  remain  as  a  black  powder  on  dissolving 
the  metal  in  acids.  The  dried  black  powder,  when  fused 
with  saltpetre,  produces  a  mixture  of  silicate  and  carbonate 
of  the  alkali.  The  metal  also  frequently  contains  copper ; 
to  test  for  this,  dissolve  the  metal  in  aqua  regia,  evaporate 
the  solution  to  a  small  bulk,  dilute  with  water  and  add 
sulphuretted  hydrogen  water;  if  a  blackish  cloud  is  not  pro- 
duced, copper  is  not  present. 

Sulphate  of  iron. — Called  also  '  green  copperas,  green 
vitriol,'  &c.  It  should  be  in  the  state  of  clear  green  crystals, 
perfectly  free  from  adhering  water  or  acid,  and  with  no  brown 
or  red  powder  about  them.  It  must  be  kept  dry,  and  in 
well-closed  bottles. 

Carbonate  of  lead. — Called  also  *  white-lead.'  It  is  a 
heavy  white  powder,  and  should  be  entirely  soluble  in  warm 
dilute  nitric  acid  ;  any  white  insoluble  matter  is  probably 
sulphate  of  barium. 

Tin.- — This  metal  is  often  adulterated  with  lead;  to 
detect  which,  cut  the  tin  up  as  small  as  possible,  digest  it  with 
warm  dilute  nitric  acid  ;  evaporate  the  clear  liquid  part  to  a 
small  bulk,  dilute  with  water,  and  add  sulphuretted  hydrogen 
water  ;  a  black  colour  or  precipitate  indicates  the  probable 
presence  of  lead  or  copper. 

Chloride  of  tin. — Called  also  '  muriate  of  tin,'  '  tin  salt,' 
'  butter  of  tin,'  '  stannous  chloride,'  &c.  This  should  be 
freshly  prepared,  in  nearly  dry  crystals  ;  and  it  should  dissolve 
entirely  in  water,  without  making  the  water  appear  milky. 
The  more  milky  the  appearance,  the  longer  has  the  salt  been 
exposed  to  the  atmosphere. 

Caustic  lime. — Called  also  '  lime,'  and  '  stone-lime.'  The 
best  quality  is  perfectly  white,  and  after  having  been  slaked, 
may  be  rubbed  to  a  soft  creamy  mixture  with  water;  gritty 
particles  consist  of  silica.  Lime  should  be  kept  in  well- 


360  The  Art  of  Electro-Metallurgy. 

closed  jars  of  stoneware  \  if  the  damp  gets  in,  the  lime  is 
apt  to  swell  and  burst  the  vessels.  Avoid  strong  building 
limes.  These,  especially  the  hydraulic  cements,  always  con- 
tain clay  or  iron  in  considerable  quantity. 

Carbonate  of  sodium. — Commonly  called  'soda,'  and 
'washing  soda.'  This  is  usually  sold  in  the  form  of  clear 
colourless  crystals,  which  lose  their  water,  and  their  trans- 
parency, by  exposure  to  dry  air,  and  fall  to  a  white  powder. 
Two  hundred  and  eighty-six  parts  by  weight  of  the  clear 
crystals,  require  fifty- six  parts  of  pure  anhydrous  caustic  lime, 
to  convert  them  wholly  into  caustic  soda. 

Caustic  potash. — Called  also  '  potash/  and  lapis  infernalis. 
This  substance  is  sold  in  several  forms,  of  different  degrees 
of  purity.  It  should  be  kept  as  much  as  possible  from 
contact  with  the  air,  because  it  rapidly  absorbs  moisture  and 
carbonic  acid.  A  solution  of  it  may  be  made,  by  converting 
fifty-six  parts  by  weight  of  pure  and  dry  caustic  lime  into 
a  cream,  by  slaking  it  with  water,  and  then  stirring  it  with 
more  water  ;  adding  the  creamy  mixture  to  138  parts  of 
anhydrous  pearlash  dissolved  in  hot  water,  and  boiling  the 
mixture  ;  the  lime  subsides  to  the  bottom  in  the  form  of  a 
carbonate.  A  purified  variety  of  caustic  potash,  is  sold  in 
the  form  of  rods  about  six  inches  in  length.  Great  care 
must  be  taken  not  to  handle  it,  as  it  is  very  caustic,  and 
makes  most  dangerous  sores. 

Carbonate  of  potassium. — Called  also  '  pearlash,'  '  salts  of 
tartar/  &c.  It  is  a  white  salt.  Strongly  alkaline  and  de- 
liquescent, and  should  be  kept  in  well-closed  bottles  or 
jars. 

Gaseous  ammonia. — This  substance  may  be  easily  pre- 
pared, by  separately  powdering,  and  then  intimately  mixing, 
equal  weights  of  dry  caustic  lime  and  sal  ammoniac,  and 
heating  the  mixture  in  a  glass  flask. 

Aqueous  ammonia.—  Called  also 'volatile  alkali/  'spirit 
of  hartshorn/  &c.  This  liquid  is  very  volatile,  and  should 
be  kept  in  well-stoppered  bottles,  in  a  very  cool  place.  Its 


Substances  iised  in  the  Art.  361 

specific  gravity  should  not  be  greater  than  *88o.  It  is  danger- 
ous to  break  the  bottles. 

Carbonate  of  ammonium. — Called  also  '  smelling-  salts,' 
'  sal  volatile.'  The  unchanged  substance  is  in  the  form  of 
transparent  colourless  pieces.  By  exposure  to  air  it  loses 
ammonia,  and  becomes  opaque  white.  It  should  therefore 
be  kept  in  well-closed  bottles. 

Hydrocyanic  acid. — Called  also  '  prussic  acid.'  This  is  a 
colourless  liquid,  consisting  of  water,  more  or  less  impreg- 
nated with  the  gas.  Water  will  dissolve  a  very  large  amount 
of  the  gas.  The  strongest  usually  sold,  is  known  as  *  Scheele's,' 
and  contains  about  5  per  cent,  of  the  actual  substance  ;  the 
ordinary  medicinal  acid  contains  only  2  per  cent  It  is 
extremely  poisonous,  and  dangerous  to  smell  or  inhale  the 
vapour  arising  from  it.  It  is  decomposed  by  light,  and 
should  therefore  be  kept  in  an  opaque  bottle,  in  a  dark  and 
cool  place. 

Cyanide  of  potassium. — Called  also  'prussiate  of  potash.' 
This  substance  also  is  a  deadly  poison,  and  almost  as 
dangerous  when  absorbed  by  the  skin,  as  when  swallowed. 
It  is  strongly  alkaline,  and  abstracts  moisture  rapidly,  and 
should  therefore  be  kept  in  well-covered  jars  or  bottles. 

Making  cyanide  of  potassium. — As  cyanide  of  potassium 
is  extensively  used  in  electro-gilding  and  electro-deposition 
generally,  and  especially  in  making  electro  silvering  baths, 
it  is  desirable  for  the  practical  depositor  to  understand  how 
it  is  made,  and  to  possess  information  respecting  -its  im- 
purities, and  the  method  of  testing  its  quality.  It  is  nearly 
always  made  by  the  following  process  : — Take  ferrocyanide 
of  potassium  (yellow  prussiate  of  potash),  well  crystallised, 
and  free  from  sulphates  ;  reduce  it  to  a  fine  powder,  and 
gently  heat  it  to  110°  or  120°  C.  in  an  iron  pan,  with  constant 
stirring,  until  quite  dry.  Heat  to  redness  a  nearly  covered 
iron  crucible  provided  with  a  lip,  put  some  of  the  dry  powder 
into  it,  and  when  that  is  melted  add  some  more,  and  so  on, 
until  the  crucible  is  three-fourths  filled,  keeping  the  crucible 


362  The  A  rt  of  Electro-Metallurgy. 

covered  as  much  as  possible  by  means  of  an  iron  lid  ;  gas 
will  be  evolved  freely  from  the  melting  salt.  Keep  the  salt 
melted  about  fifteen  minutes,  or  until  the  end  of  an  iron  rod 
dipped  into  it  shows  a  white  sample.  By  allowing  it  to  stand 
undisturbed  a  few  minutes  at  the  latter  part  of  the  operation 
and  occasionally  tapping  the  sides  of  the  crucible,  the  iron, 
&c.  which  has  separated  from  the  ferrocyanide,  will  settle  at 
the  bottom  as  a  fine  black  powder  ;  the  colourless  cyanide 
of  potassium  may  then  be  poured  off  into  a  cold  iron  pan, 
or  upon  a  thick  and  cold  iron  plate ;  it  should  be  broken 
up  whilst  still  hot,  and  preserved  in  a  well-stopped  jar.  The 
black  sediment  (which  contains  much  cyanide  of  potassium) 
should  be  scraped  out  of  the  vessel  while  still  soft,  and 
preserved,  as  water  will  at  any  time  dissolve  the  cyanide 
that  is  in  it. 

If  the  process  has  been  well  conducted,  the  product  will 
be  of  a  clear  white  colour,  or  at  most  but  very  slightly  grey. 
The  colour,  however,  is  not  a  matter  of  importance.  To 
prevent  oxidation  of  the  cyanide,  and  consequent  formation 
of  cyanate  of  potassium,  some  operators  recommend  the 
addition  of  a  few  fragments  of  charcoal,  and  a  little  powder 
of  the  same  to  the  salt,  before  it  is  entirely  melted.  The 
white  portion  of  the  product,  made  according  to  these  instruc- 
tions, contains  about  96  per  cent,  of  actual  cyanide,  and  the 
cyanide  dissolvable  from  the  black  portion,  by  means  of  cold 
water,  is  nearly  as  pure.  To  obtain  a  cyanide  of  about  70 
or  75  per  cent.,  eight  parts  of  the  dried  ferrocyanide,  mixed 
with  three  of  highly-dried  carbonate  of  potassium,  must  be 
subjected  to  similar  treatment ;  it,  however,  requires  a  less 
high  temperature  for  the  fusion.  By  this  plan,  a  larger  total 
amount  of  cyanide  of  potassium  will  be  obtained,  than  by 
the  fusion  of  the  ferrocyanide  only,  because  in  melting  the 
latter  alone,  one  third  of  the  cyanogen  escapes  as  gas  ;  but 
in  fusing  it  with  the  carbonate,  this  portion  of  the  cyanogen 
unites  with  the  potassium,  and  carbonic  acid  gas  escapes  in 
its  stead.  Cyanide  of  potassium,  from  which  the  ferruginous 


Making  and  Testing  Cyanide  of  Potassium.    363 

matter  has  not  been  completely  freed,  is  known  as  '  black 
cyanide.7  Fifty-five  parts  of  crystallised  prussiate,  become 
forty- eight  by  drying ;  and  nineteen  of  the  carbonate,  become 
eighteen  ;  and  the  sixty-six  parts  of  the  dry  mixture  yield 
about  thirty-eight  of  clean  cyanide,  besides  about  six  parts 
contained  in  the  black  sediment. 

By  experiments  with  the  commercial  white  cyanide,  I 
have  found,  that  200  grains  of  it  would  dissolve  in  230  grains 
of  distilled  water  at  60°  Fahr.,  and  that  it  was  more  soluble 
in  water  containing  hydrocyanic  acid.  The  plan  of  purifying 
cyanide  of  potassium  from  foreign  salts,  by  means  of  solution 
in  alcohol,  does  not  appear  to  effect  the  object  perfectly. 
Dr.  Schwarz  recommends  the  purification  of  it  from  carbonate 
and  cyanate  of  potassium,  by  digesting  it  in  bisulphide  of 
carbon,  and  recovering  the  solvent  by  distillation  (see 
*  Chemical  News,'  vol.  viii.  p.  51);  but  this  appears  to  be 
an  unlikely  process. 

Testing  cyanide  of  potassium. — According  to  Glassford 
and  Napier,  the  quantity  of  pure  cyanide  in  any  given  sample 
of  cyanide  of  potassium,  may  be  correctly  ascertained  thus — 
Make  two  solutions,  one  of  the  cyanide,  and  one  of  nitrate 
of  silver,  each  containing  known  weights  of  the  salts,  say  one 
ounce  of  the  cyanide  dissolved  in  distilled  water  in  a  gradu- 
ated glass  vessel,  so  as  to  form  six  ounces  by  measure  of 
solution  ;  and  175  grains  of  the  crystallised  nitrate,  dissolved 
in  about  two  or  three  dunces  of  distilled  water  ;  add  the 
cyanide  solution  carefully  and  slowly  to  the  nitrate  of  silver 
liquid,  with  continual  stirring,  until  the  precipitate  first 
formed  is  exactly  all  re-dissolved.  The  amount  of  the  solu- 
tion required  to  effect  this,  with  the  above  quantity  of 
nitrate  of  silver,  will  have  contained  130  grains  of  pure 
cyanide,  and  from  the  quantity  used,  we  may  easily  calculate 
the  amount  of  pure  cyanide  in  the  whole  ounce.  It  is  said 
by  the  authors,  that  '  when  nitrate  of  silver  is  added  to  a 
solution  of  cyanide  of  potassium,  so  long  as  the  precipitate 
formed  is  all  re-dissolved,  we  obtain  the  whole  of  the  cyanide 


3  64  The  A  rt  of  Electro-Metallurgy. 

of  potassium  in  combination  with  the  silver  :  none  of  the 
other  salts  in  solution  take  any  part  in  the  action,  even  though 
they  be  present  in  a  large  proportion.  This  enables  us  to  test 
the  exact  quantity  of  cyanide  of  potassium  in  any  sample.' 

I  have  employed  this  process  on  many  occasions,  and 
have  found  from  28  to  96  per  cent,  of  actual  cyanide  in 
different  samples.  In  what  is  termed  '  black  cyanide '  I  have 
found  from  17*65  to  23-40  per  cent,  of  black  insoluble 
matter,  and  of  soluble  salts,  not  cyanide,  from  5*21  to  5-43 
per  cent,  and  in  a  grey  specimen  1-35  per  cent,  of  black  solid 
matter,  and  1875  Per  cent,  of  soluble  salts  not  cyanide.  This 
black  substance  burned  in  a  flame  like  iron  filings,  evolved 
an  inflammable  gas  by  addition  of  dilute  sulphuric  acid  ;  and 
after  digestion  in  dilute  hydrochloric  acid,  much  black  com- 
bustible powder  was  left :  it  doubtless  consists  of  iron  and 
carbon.  The  other  impurities  consist  of  carbonate,  sulphide, 
chloride,  cyanate,  ferrocyanide  of  potassium,  and  silica.  The 
chloride  of  potassium  is  derived  from  the  original  salts,  and 
the  sulphide  from  sulphate  of  potassium  contained  in  them  ; 
the  silica  occurs  when  the  cyanide  is  made  in  an  earthen 
crucible  ;  and  even  when  the  process  is  well  conducted,  and 
pure  materials  used,  the  product  sometimes  contains  20  per 
cent,  of  cyanate  of  potash,  produced  partly  by  the  contact  of 
the  air  with  the  melted  mixture.  The  presence  of  even  a 
small  quantity  of  sulphates  in  the  materials,  is  said  to  impart 
to  the  cyanate,  a  blue,  green,  or  pink  colour ;  probably  in 
consequence  of  the  production  of  an  alkaline  sulphide. 
The  price  of  cyanide  varies  from  about  2s.  6d.  to  $s.  per 
pound. 

Ferrocyanide  of  potassium. — Called  also '  yellow  prussiate 
of  potash.'  This  salt  is  in  the  form  of  large  clear  yellow 
crystals,  and  is  used  for  making  the  simple  cyanide  of  potas- 
sium. 

Acetate  of  copper. — Called  also  '  crystallised  verdigris/  It 
is  in  the  form  of  dark  green  crystals,  soluble  in  water. 
Common  verdigris  is  in  lumps  or  powder  of  a  bluish  colour, 


Siibstances,  etc.,  used  in  the  Art.  365 

and  contains  a  larger  proportion  of  copper,  but  is  insoluble  in 
water  :  it  dissolves  in  diluted  acetic  acid,  and  then  forms  the 
same  liquid  as  the  solution  of  crystallised  verdigris. 

Acetate  of  lead. — Known  also  as  '  sugar  of  lead/  It  is  a 
colourless  crystalline  salt,  with  an  appearance  like  that  of 
loaf-sugar.  It  should  be  entirely  soluble  in  distilled  water ; 
if  it  is  not  so,  add  a  small  quantity  of  acetic  acid  (wood- 
vinegar). 

Test-papers. — The  most  useful  variety  of  these,  is  neutral- 
tint  litmus  ;  the  red  and  blue  kinds  may  also  be  employed. 

Thermometers  and  Hydrometers. — The  operator  will  also 
require  a  couple  of  thermometers,  and  several  hydrometers ; 
the  latter  should  be  suitable  for  testing  the  specific  gravity, 
both  of  aqueous  ammonia,  and  of  strong  sulphuric  acid. 

Syphons. — The  most  convenient  are  pieces  of  tubing  of 
glass,  gutta-percha,  or  lead,  bent  to  the  proper  forms  ;  or  a 
piece  of  india-rubber  tubing.  To  cause  them  to  act,  they 
should  be  filled  with  the  liquid  to  be  decanted,  the  ends 
closed  by  the  fingers,  and  then  inverted,  with  the  shortest 
leg  plunged  into  the  liquid. 

Filters. — Small  ones  for  filtering  dilute  acids  or  alkalies, 
and  liquids  generally,  are  made  by  doubling  a  circular  sheet 
of  filtering-paper  (i.e.  unsized  or  blotting-paper)  twice  at 
right  angles,  opening  one  of  the  outer  folds,  and  placing  the 
filter  in  a  glass  funnel.  Large  ones  are  usually  formed  by 
tying  or  nailing  the  edges  of  a  piece  of  washed  or  unglazed 
calico  to  those  of  a  square  frame  of  wood,  or  of  a  wooden 
hoop.  A  filter  for  strong  acids  or  alkalies,  is  made  by 
placing  a  loose  plug  of  asbestos  in  the  neck  of  a  glass  funnel, 
or  by  filling  the  neck  of  the  vessel  with  broken  glass,  and 
covering  the  latter  with  a  layer  of  asbestos. 


366  The  A  rt  of  Electro-Metallurgy. 


REMEDIES  FOR  ACCIDENTS,  ETC.,   IN  PROCESSES  OF 
E  LE  CTRO-METALL  URG  Y. 

As  various  poisonous  substances  are  employed  in  the  art, 
it  would  be  well  for  the  operator  to  know  their  best  anti- 
dotes. If  either  nitric,  hydrochloric,  or  sulphuric  acid  have 
been  swallowed,  the  best  remedies  are,  either  to  administer 
abundance  of  tepid  water  to  act  as  an  emetic,  or  to  cause 
the  patient  to  swallow  milk,  the  whites  of  eggs,  some  calcined 
magnesia,  or  a  mixture  of  chalk  and  water.  If  those  acids 
in  a  concentrated  state,  have  been  spilled  upon  the  skin, 
the  parts  should  be  washed  with  plenty  of  cold  water  ;  and, 
if  necessary,  a  mixture  of  whiting  and  olive-oil  then  applied. 
A  useful  mixture  for  such  cases  is  formed  by  slaking  about 
an  ounce  of  caustic  lime  with  a  quarter  of  an  ounce  of  water, 
then  adding  it  to  a  quart  of  water  and  shaking  the  mixture 
repeatedly ;  decanting  the  clear  liquid,  and  beating  it  up  with 
olive-oil  to  form  a  thin  pomatum.  Acids  spilled  upon  the 
clothes,  should  at  once  be  treated  with  plenty  of  a  quite 
dilute  solution  of  ammonia  or  its  carbonate,  and  then  well 
washed  with  water. 

In  cases  where  hydrocyanic  acid,  cyanide  of  potassium, 
or  the  ordinary  silvering  or  gilding  solutions  have  been 
swallowed,  almost  instant  death  usually  follows  ;  if  it  does 
not,  very  cold  water  should  be  allowed  to  run  upon  the  head 
and  spine  of  the  sufferer,  and  the  patient  be  made  to  swallow 
a  dilute  solution  of  either  acetate,  citrate,  or  tartrate  of  iron. 
If  the  poisoning  arises  from  inhaling  the  vapour  of  hydro- 
cyanic acid,  cold  water  should  be  applied  as  above,  and 
the  patient  be  caused  to  inhale  atmospheric  air  containing  a 
little  chlorine  gas.  It  is  a  dangerous  practice  to  dip  the 
naked  hands  or  arms  into  cyanide  solutions,  (as  workmen 
sometimes  do,  in  order  to  recover  articles  which  have  fallen 
into  them,)  because  those  liquids  are  absorbed  by  the  skin, 


Remedies  for  Accidents.  367 

and  produce  poisonous  effects  ;  they  also  cause  very  painful 
sores,  which  should  be  well  washed  with  water,  and  the 
mixture  of  lime-water  and  olive-oil  applied. 

If  alkalies,  such  as  potash  or  soda,  have  been  swallowed, 
a  dilute  solution  of  vinegar,  some  lemonade,  or  extremely 
dilute  sulphuric  acid,  should  be  given ;  and,  after  about  ten 
minutes,  a  few  spoonfuls  of  olive  oil. 

If  metallic  salts  have  been  taken,  the  patient  should  be 
made  to  vomit  by  means  of  tepid  water,  and  then  to  swallow 
some  milk,  whites  of  eggs,  precipitated  sulphur,  or  some  sul- 
phuretted hydrogen  water. 

To  remove  stains  of  sulphate  of  copper,  or  of  salts  of 
mercury,  silver,  or  gold,  from  the  hands,  etc.,  wash  them  first 
with  a  dilute  solution,  either  of  ammonia,  iodide,  bromide,  or 
cyanide  of  potassium,  and  then  with  plenty  of  water ;  if  the 
stains  are  old  ones,  they  should  first  be  rubbed  with  the 
strongest  acetic  acid,  and  then  treated  as  above. 

Grease,  oil,  pitch,  or  tar,  may  usually  be  removed  from 
the  hands,  clothes,  etc.,  by  rubbing  with  a  rag  saturated  with 
benzine,  spirits  of  turpentine,  or  bisulphide  of  carbon. 


APPENDIX. 


LIST  OF  BOOKS  ON   ELECTRO-DEPOSITION. 

1841.     Galvanoplastik  Art,  by  Dr.  M.   H.  Jacobi,  translated  by  W. 
Sturgeon. 

1843.  Elements  of  Electro- Metallurgy,  2nd  Edition.    A.  Smee,  F.R.S. 

1844.  Manual  of  Electro- Metallurgy,  2nd  Edition.     G.  Shaw,  F.G.S. 

1853.  Electro-type  Manipulation,  Part  I.  l6th  Edition,  Part  II.  29th 

Edition.     C.  V.  Walker. 

1854.  Galvanoplastie.     Encyclopedie  Roret.     2  vols.      Paris. 

1855.  Theory  and  Practice  of  Electro-Deposition.     G.  Gore. 

1856.  Repertorium  der  Galvanoplastik  und  Galvanostegie.     A.Martin. 

2  vols.     Vienna  :  Carl  Gerold's  Sohn. 
1862.     Les  Depots  Metalliques.     Henri  Bouilhet.     Paris  :  Bonaventura 

et  Ducessois. 
1862.     De  VOrfevrerie  Electro-chimique.     V.  Meunier.     Paris  :  Savy. 

1862.  Die  Galvanische   Vergoldung  und  Versilberung.     W.  E..  Rab. 

Leipzig  :  Abel. 

1863.  History  of  Electro- Metallurgy.     H.  Dircks. 

1866.  Elements  cTElectro-chimie.     M.  Becquerel.     Paris. 

1867.  Die   Galvanoplastik.     G.  L.  v.  Kress.     Frankfort  am  Maine  : 

Boselli. 

1868.  Katechismus der  Galvanoplastik.  T.  Martius-Matzdorff.  Leipzig. 
1870.     Die  Galvanoplastik.     A  Hering.     Leipzig  :  Waldow.   . 

1870.     Electro-chimie.     N.  A.  Renard.     Nancy  :  Lordoillet  et  Fils. 
1870.     Nouveau  Manuel  Complet   de   Donire.      Paris  :    Matthey  et 

Maigne. 
1870.      The  Electrotyper?  Manual.     Buffalo  :  W.  S.  Spiers. 

1872.  Galvano-plastic  Manipulation.     A.  Roseleur. 

1873.  Kunst  des  Vergoldens.     C    H.  Schmidt.     Weimar  :  Voigt. 

1873.  HydropListie,  Electro-chimie,  Galvanoplastie.     A.  de  Plazanet. 

Paris  :  Lacroix. 

1874.  Electro- Metallurgy,  5th  Edition.     A.  Watt. 

B  B 


37O  Appendix. 

1876.     Manual  of  Electro- Metalhirgy.,  5th Edition.  J.Napier,  F.R.S.E. 
1876.     Handbuch  der   Galvanoplastik.     Von  G.   Kaselowsky.     Stutt- 
gard  :  Riegerische  Verlagsbuchhandlung. 

1878.  Journal  of  Electrotypy,  published  in  Chicago. 

1879.  Katechismus  der  Galvanoplastik.     Von  G.  Seelhorst.     Leipzig: 

J.    J.  Weber. 

1880.  The  Electro-Metallurgist,   a  periodical.    London  :  Brock  &  Co. 
1880.     Stereo-typing  and  Electro-typing.     London:  F.  T.  F.  Wilson. 

1880.  Electro-plating.     J.  WT.  Urquhart. 

1 88 1.  Electro-typing.     J.  W.  Urquhart. 

1 88 1.     La  Galvanoplastie,  Electro-chimique  sur  Metaux.     G.  Marius. 

Orleans  :  Puget  et  Cie. 

1 88 1.     Manuel  de  Galvanoplastie.     Madrid:  L.  Monet. 
1 88 1.     Das    Galvaniseren   von   Metallen.     W.  Pfanhauser.      Vienna : 

Lehmann  und  Wentzel. 
1 88 1.     Das  Verzinnen,  Verzinken,  Vernickeln.  F.  Hartmann.  Vienna  : 

Hartleben. 

1881.  Manuel  de  Galvanoplastie.     Ferrini.     Milano :  Hoepli. 

1882.  Electro- Metallurgy.     By  C.  Alker.     Brussels  :  C.  Marquardt. 

1883.  Die   Electrolyse,    Galvanoplastik    und    Reinmetallgeivinnung. 

Von  Edward  Japing.     Vienna  :  Hartleben. 

1883.     Die  Galvanoplastik.     Von  Julius  Weiss.      Vienna  :  Hartleben. 
1883.     Katechismus  der  Electrotechnik.     Von  Th.  Schwarze.    Leipzig  : 

J.  J.  Weber. 
1883.     Die  Elektrolyse.     Von  Dr.  Hans  Jahn.     Vienna  :  A.  Holder. 

In  addition  to  the  above  there  are  : — Art  of  Electro-typing,  by 
Sturgeon  ;  Instructions  for  tJie  Multiplication  of  Works  of  Art  by  Voltaic 
Electricity,  by  Spencer  ;  Manuel  Complet  de  Galvanoplastie,  by  M.  L. 
de  Valicourt,  2  vols.  ;  Traite  de  Galvano-plastie,  by  J.  L.  ;  Manuel  de 
Dorure  et  d1  Argentiire  par  la  MetJwde  Ele.ctro-chimique  et  par  Simple 
Immersion,  by  MM.  Selmi  and  Valicourt.  Chapters  on  electro- 
deposition,  in  Gmelin's  Handbook  of  Chemistry,  vol.  I.  Birmingham 
and  Midland  Hardware  District  (Hardwicke),  1865,  pp.  477,  510. 
Sprague's  Electricity  (Spon  and  Co.),  1875,  P-  2^7-  British  Mami- 
facturing  Industries  (Stanford),  1876,  p.  137.  Applications  of  the  Physical 
Forces,  by  A.  Guillemin,  translated  by  Mrs.  Lockyer,  1877,  p.  701. 
Also  a  very  large  number  of  original  articles  on  different  parts  of  the 
subject,  scattered  through  the  pages  of  various  scientific  periodicals, 
to  which  references  have  already  been  made  in  the  body  of  this  book. 


Appendix.  371 


LIST   OF   PATENTS   RELATING   TO   ELECTRO- 
METALLURGY. 

1836.  June  24.     G.  R.  Elkington.     Gilding  copper,  brass,  and  other 

metals. 

1837.  February  17.     H.  Elkington.     Coating  metals  with  gold  and 

platinum. 

„  December  4.  H.  Elkington.  Gilding  and  silvering  certain 
metals. 

1838.  July  24.     G.  R.  Elkington  and  O.  W.  Barratt.    Coating  copper 

and  brass  with  zinc. 

1840.  March  3.     J.  Shore.     Coating  metals  with  copper  and  nickel. 
„        March  25.     G.   R.  and  H.  Elkington.     Electro-silvering  and 

gilding  in  cyanide  solutions. 
,,        August    15.     No.  8604.      V.   A.  Fontainemoreau.      Coating 

metals  and  alloys  with  silver,  gold,  platinum,  &c. 
,,         October  7.     T.  Spencer  and  J.  Wilson.     Voltaic  etching. 
,,        December  17.     W.  T.  Mabley.       Producing  printing  surfaces. 

1841.  January  14.     A.  Jones.     Making  copper  vessels.     Rendering 

surfaces  conductible. 

„  February  8.  No.  8842.  W.  H.  F.  Talbot.  Electrotype  and 
photography, 

,,  March  8.  T.  Spencer.  Making  picture-frames.  Depositing 
gold,  silver,  platinum,  and  tin. 

,,        March  29.     A.  Parkes.     Production  of  works  of  art. 

,,  September  8.  O.  W.  Barratt.  Deposition  of  copper  (from 
mineral  waters),  silver,  gold,  platinum,  palladium,  and 
zinc. 

„  December  9.  W.  H.  F.  Talbot.  Gilding,  silvering,  orna- 
menting, &c.  Use  of  alkaline  hyposulphites. 

1842.  January  15.     E.  Palmer.      Producing  printing  and  embossing 

surfaces  (glyphography). 

„  June  i.  H.  B.  Leeson.  Electro-depositing  processes.  '  Gela- 
tine moulds  ; '  '  positive  wires  ; '  '  guiding  wires  ; '  keeping 
articles  in  motion  ;  cleaning  articles,  '  quicking '  their  sur- 
faces. Claims  430  different  salts. 

„        June  4.     E.  Tuck.     Deposition  of  silver. 

„  August  i.  J.  S.  Woolrich.  Plating  by  means  of  magneto- 
electricity.  Use  of  alkaline  sulphites. 

ft        W.  H,  F.  Talbot.     Electro-gilding  and  silvering. 

B  B  2 


372  Appendix. 

1843.  April  II.  J.Napier.    Depositing  copper  upon  fibrous  materials. 
,,        May  4.     No.  9720.    E.  Morewood  and  G.  Rogers.    Depositing 

tin  upon  iron  and  other  metals. 
,,        May  25.     M.  Poole.     Plating  by  means  of  thermo-electricity. 

Gold,  silver,  and  copper  solutions. 
,,        June  15.     O.  W.  Barratt.     Depositing  gold,  silver,  platinum, 

palladium,  lead,  &c. 
,,        November  21.      No.    9,957.     A.  F.  J.   Claudet.     Producing 

printing  surfaces  from  daguerreotypes. 
,,        Decembers.     J.  Schottlaender.    Electro-depositing  upon  felted 

fabrics. 

1844.  February  21.     No.  10,063.     A.  Parkes.     Deposition  of  metals 

and  alloys. 

»»  July  31-  No.  10,282.  P.  A.  Fontainemoreau.  Electro- 
brassing. 

,,         October  22.    J.Napier.    Depositing  metals  from  fused  minerals. 

,,  October  29.  A.  Parkes.  Depositing  gold  and  silver  from  their 
melted  salts. 

1845.  October  9.     A.  Parkes.     Embellishing  metals.     . 

1846.  January  29.     No.  11,065.     G.  Howell.     Coating  metals  with 

platinum. 

,,  December  12.  L.  H.  Piaget  and  P.  H.  Du  Bois.  Depositing 
gold,  silver,  and  copper. 

1847.  March  23.     M.  Lyons  and  W.  Milward.     Bright  silver  depo- 

sition. 

,,  August  3.  T.  Fletcher.  Depositing  silver  and  copper  upon 
the  backs  of  glass  mirrors. 

,,  September  9.  J.  C.  Robertson.  Separating  sulphur,  phos- 
phorus, &c.  from  melted  minerals. 

,,  September  30.  C.  De  la  Salzede.  Deposition  of  brass  and 
bronze  upon  iron,  &c. 

,,        November  4.     C.  M.  T.  Du  Motay.     Inlaying  metals. 

1848.  January  13.     S.E.Morse.     Production  of  printing  surfaces. 

1849.  March  14.     P.  A.  Fontainemoreau.       Deposition  of  platinum, 

gold,  silver,  copper,  brass,  tin,  and  lead. 
,,        March  19.     T.  H.  Russell  and  J.  S.  Woolrich.     Deposition  of 

cadmium  and  of  alloys. 
,,        March  26.     A.   Parkes.     Depositing  printing-rollers,   copper, 

silver,  bismuth,  tin,  and  lead. 

1850.  March  23.     A.  G.  Roseleur.     Deposition  of  tin. 

,,        August  9.    J.  Steele.    Gilding,  silvering,  bronzing  and  brassing 

1851.  February  17.     C.  Cowper.     Elastic  moulds. 


Appendix.  373 

1851.  May  3.     No.  13,620.     W.  Cooke.     Making  soda  and  its  car- 

bonate. 

„  August  23.  No.  13,726.  J.  Palmer.  Gelatine  moulds  for 
electrotype. 

,,  September  25.  C.  Watt.  Depositing  alkali  metals.  Sepa- 
rating and  purifying  metals. 

1852.  April  20.     J.  Ridgway.     Coating  glass  and  china. 

,,        August  26.     A.  Crosse.     Separating  copper  from  its  ores. 

,,         October  I.     W.  Potts.     Making  sepulchral  monuments. 

,,         October  2.     J.  J.  Rousseau.      Making  door-plates. 

,,         October  12.     F.  Michel.     Stereotyping  in  copper. 

,,         October  21.       J.   Bernard.      Depositing  printing  surfaces  for 

ornamenting  leather. 

,,        November  13.     W.  Petrie.     Refining  metals. 
,,         November  29.     J.  D.  Schneiter.     Producing  maps. 
,,         November  30.     W.  Jeffs.     Making  letters,  figures,  &c. 
,,         December  II.     T.  Morris  and  W.  Johnson.     Depositing  brass 

and  other  alloys. 
,,        December  n.     C.    Griffin.     Obtaining  copper  from  mineral 

waters. 
,,        December  28.      C.  J.  Junot.      Depositing  silicium,  titanium, 

tungsten,  chromium,  and  molybdenum. 
,,        December  29.     J.  Power.     Silvering  glass,  &c. 
I^53-     January  i.     J.  J.  W.  Watson  and  W.  Prosser.      Depositing 

carbon  into  iron  to  form  steel. 
,,        May  ii.     W.  Bradbury  and  F.  M.  Evans.     Preparing  printing 

surfaces. 
,,        July  29.     W.  E.  Newton.     Depositing  metals,  bronze,  brass, 

and  an  alloy  of  manganese  and  zinc. 
,,        August   5.      No.    1,836.     W.    Newton.      Coating  iron   with 

metals  and  alloys  (brass). 

,,         October  7.     W.  Ellis.     Ornamenting  china  and  porcelain. 
,,         October  8.     W.  Potts.     Ornamenting  mantelpieces. 
,,        November  7.     H.  Pershouse  and  T.  Morris.    Depositing  metals 

and  alloys. 

1854.     January  ii.     A.  R.  Brooman.     Extracting  gold  from  its  ores. 
,,        January  19.     G.  H.  Burrill.     Extracting  metals  from  minerals, 

slag,  and  jewellers'  refuse. 

,,        January  30.     W.  Phillips.     Making  coffins. 
,,         February  I.     R.  and  J.  Jobson.     Making  moulds  for  casting 

metals. 
„         February  28.     T.  Denny.     Improvements  in  engraving. 


374  Appendix. 

1854.  March  20.     J.  Perkins.     Making  printers'  type. 

,,         April  13.     G.  Devincenzi.     Making  printing  surfaces. 

,,         April  20.     J.  Reed.     Extracting  metal  from  amalgams. 

,,        April  27.     C.  C.  Person.     Coating  with  /inc. 

,,        July  4.     J.  H.  Johnson.     Coating  iron  with  lead  or  copper. 

,,        July    15.     M.   F.   Wagstafife  and  J.   W.   Perkins.     Extracting 

metals  from  their  ores. 
,,        July   1 8.      P.   A.   Fontainemoreau.      Etching  zinc  plates  for 

printing. 

,,        July  29.     A.  E.  L.  Bellford.     Electro-engraving. 
,,         November  4.     P.  Pretsch.     Making  copper  plates  for  printing. 
,,         December  21.     J.  H.  Johnson.     Making  statuettes. 
,,         December   26.      F.   S.  Thomas  and  W.   E.  Tilley.     Coating 

metals  with  tin,  nickel,  or  aluminium. 

1855.  January  3.     J.  H.  Johnson.     Coating  iron  with  copper. 

,,         February  3.     F.  S.  Thomas  and  W.  E.  Tilley.     Deposition  of 

silver,  copper,  nickel,  and  tin. 

,,        February  13.     R.  Cornfield.     Coating  iron  with  zinc. 
,,         March  17.     T.  Petitjean  and  L.  Petre.     Making  daguerreotype 

plates,  &c. 

,,         April  2.     G.  W.  Friend.     Improvements  in  umbrellas. 
,,         April    n.     L.   and  A.   Oudry.     Preserving  wood,  metal,  and 

other  substances, 

,,        June  5.     F.  Puls.     Coating  iron  with  zinc. 
,,        July  10.     C.  J.  C.  Elkington.     Depositing  alloys  of  nickel  and 

silver,  &c. 
,,        July  21.     P.  A.   Fontainemoreau.      Depositing  copper  upon 

carbon. 

,,         September  4.     J.G.Taylor.     Deposition  of  aluminium. 
,,         October  4.     No.  2,215.     H.  Cornforth.     Electro-coating  hooks 

and  eyes. 

,,        October  12.     F.  Puls.     Deposition  of  zinc  upon  iron. 
,,         October  25.     J.  A.  Richards.     Making  embossing  surfaces  for 

ornamenting  leather. 

,,         November  14.     A.  V.  Newton.     Making  surfaces  for  printing. 
,,         December  3.     A.  Watt.     Coating  iron  and  steel  with  zinc. 
,,        December  6.     F.   S.   Thomas  and  W.  E.  Tilley.     Depositing 

aluminium  and  its  alloys. 

1856.  January  I.     J.  Calvert.     Extracting  metals  from  minerals, 

,,        January  12.      C.  Oudry.      Preserving  metals  and  other  solids. 
,,        February  14.      E.  More  wood  and  G.   Rogers.     Deposition  of 


Appendix.  375 

1856.  March    10.      L.    Chablin   and   A.    Hennique.      Ornamenting 

china,  &c. 

,,  March  25.  G.  and  H.  Cottam.  Ornamenting  chairs  and  bed- 
steads. 

,,        April  3.     J.  H.  Glassford.     Preparing  surfaces  for  printing. 

,,         April  15.    No.  899.    E.  R.  Southby.    Coating  iron  with  copper. 

„        June  4.     R.  A.  Brooman.       Electro-plating  upon  glass. 

,,        October  25.     G.  Ernst  and  W.  Lorberg.     Electro-etching. 

,,  December  3.  No.  2,871.  J.  K.  Cheatham.  Electro-deposi- 
tion with  photography. 

,,  December  17.  C.  Cowper.  Deposition  of  silver  and  copper 
upon  base  metals. 

1857.  January  i.     E.  T.  Noualhier  and  J.  B.  Prevost.    Coating  glass, 

corpses,  &c.  with  gold,  silver,  copper,  platinum,  or  iron. 
,,        January  19.     J.  H.  Johnson.    Improvements  in  galvano-plastic 

processes. 

,,        January  22.     J.  Rubery.    Electro-brassing  the  ribs  of  umbrellas. 
,,        January  27.     No.  240.     G.  T.  Bousfield.    Coating  metals  with 

tin. 

,,        March  II.     J.  D.  Cooper.     Making  printing  surfaces. 
,,         March  13.     E.  J.  N.  Juvin.     Making  surfaces  for  printing. 
,,        March  31.     S.  Goode.     Depositing  alloys. 
,,        April  25.     J.   Burrow.     Coating   wrought   iron   with   copper 

lead,  tin,  or  zinc. 

,,         April  27.     C.  Cowper.     Depositing  gold  and  silver. 
,,         May  7.     D.  Morrison.     Making  printing  rollers. 
„        June  I.     W.  H.  Walenn.      Depositing  gold,   silver,    copper, 

bronze,  and  brass. 

,,        June  24.     No.  1,766.    A.  Parkes.    Coating  metals  with  metals. 
,,        July  I.     W.  E.  Newton.     Producing  printing  surfaces. 
»>        July  30.     S.  Coulson.     Deposition  of  aluminium. 
j>        Juty  3°'     W.  McKinley  and  R.  Walker.     Making  moulds  of 

soles  of  boots  and  shoes. 

,,         September  21.     G.  Schaub.     Making  printing  cylinders. 
,,        October  16.     J.  Chadwick.     Making  printing  rollers. 
,,        December  19.     T.  Newey,  J.   Corbett,  and  W.   II.  Parkes. 

Tinning  steel-pens. 

1858.  January  19.     No.  93.     Otto  von  Corvin.     Inlaying  and  orna- 

menting metals. 
,,  February  19.  No.  317.  J.  M.  Syers.  Extracting  metals 

from  their  ores. 
„  February  22.  No.  341.  G.  Schaub.  Making  printing  types. 


376  Appendix. 

1858.  February  23.     No.  353.     E.  C.  Shepherd.     Depositing  metals 

and  alloys. 

,,  March  12.  No.  507.  L.  F.  Corbelli.  Deposition  of  alu- 
minium. 

,,  March  22.  No.  594.  G.  Davies.  Metallisation  of  objects 
for  electrotype. 

„  March  29.  No.  667.  E.  A.  Jacquin.  Coating  printing  sur- 
faces with  iron. 

,,  April  10.  No.  785.  A.  C.  Thibault.  Making  moulds  for 
printing  paper-hangin  ^s. 

,,         April  1 6.     No.  831.    J.H.Johnson.    Making  printing  surfaces. 

,,  June  3.  No.  1,255.  Baron  Justus  Liebig.  Protecting  backs 
^•of  mirrors. 

,,  June  8.  No.  1,289.  R.  A.  Brooman.  Manufacture  of  copper 
pipes. 

,,  June  22.  No.  1,406.  G.  Schaub.  Making  door-plates,  sign- 
boards, letters,  £c. 

,,  September  27.  No.  2,161.  W.  Lander.  Engraving  and 
printing. 

,,  October  23.  No.  2,371.  J.  C.  Martin.  Manufacture  of  metal 
moulds,  &c. 

,,         October  28.     No.  2,409.     W.  Munro.     Making  capsules,  &c. 

,,  December  16.  No.  2,890.  R.  A.  Brooman.  Plating  and 
gilding  forks  and  spoons. 

1859.  January  12.    No.  fo3.    C.  Beslay.    Depositing  tin,  zinc,  or  lead. 
,,         February  5.     No.  333.     R.  Tinkler.    Improvements  in  churns. 
,,        February    17.       No.    444.       B.     Saillard.      Making    printing 

plates. 

,,  April  26.  No.  1,044.  W.  Mackenzie.  Making  printing  sur- 
faces. 

,,  April  30.  No.  1,083.  J.  Toussaint.  Moulds  and  moulding 
for  deposition. 

,,         August  29.     No.  1,964.     G.  Edwards.     Coating  buttons. 

,,  September  14.  No.  2,095.  C.  Beslay.  Making  printing  sur- 
faces. 

,,         December  6.     No.  2,764.     F.  Potts.     Making  tubes. 

1860.  January  25.     No.    187.      T.    Rampacher  and  C.    F.    Schmidt. 

Coating  wire  gauze. 
,,        January  26.     No.   204.     W.   E.   Newton.     Depositing  crystal 

gold. 
,,        February  21.     No.    469.      L.    Sautter.       Coating  mica   with 

metal  for  reflectors. 


Appendix.  377 

1860.  March  10.     No.  653.     T.  Morris.     Improvements  in  vats  for 

depositing. 

,,  March  22.  No.  748.  G.  T.  Peppe.  Coating  lead  with 
tin. 

,,  April  9.  No.  893.  L.  Eidlitz.  Producing  printing  sur- 
faces. 

,,  May  1 6.  No.  1,209.  C.  M.  Guillemin.  Coating  telegraph 
cables  with  copper. 

,,  June  6.  No.  1,385.  E.T.Hughes.  Coating  type  and  stereo- 
type. 

,,  June  22.  No.  1,523.  N.  Grattan.  Gilding  steel  and  other 
metals. 

,,  July  25.  No.  1, 800.  M.  A.  F.  Mennons.  Etching  surfaces 
for  printing. 

1 86 1.  January  7.     No.  44.     W.  Bagley  and  W.  Mincher.     Coating 

metals. 

,,  January  19.  No.  145.  B.  Piffard.  Preparing  non-conducting 
surfaces  for  deposition. 

,,        March  13.     No.  619.     J.  Cimeg.     Silvering  glass,  &c. 

,,  May  13.  No.  1,214.  T.  Bell.  Coating  metals  with  alu- 
minium. 

,,  May  17.  No.  1,259.  S.  Tearne.  Producing  designs  on  metal 
articles. 

,,  June  8.  No.  1,469.  W.Clark.  Rendering  casks,  &c.,  water- 
tight. 

,,  July  1 6.  No.  1,792.  C.  D.  Abel.  Depositing  nickel,  and 
making  alloys. 

,,  August  3.  No.  1,936.  J.  Lewis.  Making  surfaces  for 
printing. 

„  August  14.  No.  2,023.  R-  A.  Brooman.  Coating  wire  with 
gold,  silver,  copper,  &c. 

,,  August  15.  No.  2,040.  J.  Faucherre.  Making  gold 
dials. 

,,  No.  2,314.  J.  Cimeg.  Depositing  silver  and  other  metals 
on  textile  fabrics. 

M  October  9.  No.  2,521.  H.  B.  Coathupe  and  F.  H.  Waltham. 
Making  embossed  surfaces. 

,,        No.  2,675.     A.  Dalrymple.     Depositing  metals. 

,,  October  28.  No.  2,699.  W.Clark.  Producing  printing  sur- 
faces. 

,,  November  5.  No.  2,784.  G.  T.  Bousfield.  Depositing  metals 
from  concentrated  solutions  of  cyanides. 


378  Appendix. 

1861.  November  23.     No.  2,944.     J-  Weens.     Making  metal  tubes, 

and  coating  metals. 
,,         December  7.     No.   3,074.     T.   Fearn  and  T.   Cox.     Coating 

the  metal  parts  of  umbrellas,  &c. 
„        December  9.     No.  3,081.     M.   A.    F.   Mennons.     Producing 

designs  for  printing  and  embossing,  &c. 
,,        December  17.     J.   B.  Bunney  and  T.  Wright.     Ornamenting 

bedsteads  and  other  articles. 

1862.  February  22.     No.  469.     H.  Chavasse,  T.  Morris,  and  G.  B. 

Haines.     Ornamenting  bedsteads  and  other  articles. 
,,        April  19.     No.  149.     A.  Parkes.     Coating  surface  condensers 

with  silver. 
,,        May  20.     No.   1,528.     W.   Petrie.     Improvements  in  vessels 

for  boiling  acids,  &c. 
,,        May  21.     No.    1,538.     W.   E.   Newton.     Making  metallised 

fabrics  or  surfaces. 

,,        June  28.     No.  1,896.     C.  Beslay.     Coating  metals. 
,,        July  17.     No.  2,044.     J.  Dickson.     Making  soda. 
,,        July  24.     No.  2, 101.      J.  Dickson.      Extracting  copper  from 

ores  and  solutions. 
,,        August  12.     No.  2,253.   J.  Dickson.    Extracting  zinc  from  ores 

and  solutions. 
,,        August  12.     No.  2,254.     J.   Dickson.     Extracting  lead  from 

ores  and  solutions. 

„        August  13.     No.  2,265.     J.  Dickson.     Making  chlorine. 
,,        August  13.     No.  2,266.     J.  Dickson.     Deposition  of  sodium, 

with  electrodes  of  carbon. 
,,        August  1 8.     No.  2,314.   J.  Cimeg.   Depositing  silver  and  other 

metals. 
,,        August  30.     No.  2,410.   J.  H.  Johnson  (from  C.  F.  L.  Oudry). 

Coating  surfaces  with  copper. 
„        September  9.     No.  2,479.     J-  Maurice.     Coating  the  bottoms 

of  ships  with  copper. 

,,         October  3.     No.    2,675.     A.  Dalrymple.     Depositing  metals. 
,,         November  4.     No.  2,988.     A.  Wall.     Purifying  lead. 

1863.  January   20.     No.    171.      H.    A.    Bonneville.      Ornamenting 

electro-deposited  articles. 
,,        January  21.      No.    180.     F.   A.  Busch.      Making  vessels  for 

containing  liquids. 
„        February  25.     No.  529.     W.  E.  Newton.     Making  stereotype 

plates. 
,,        March  26.     No.  795.     G.  Davies.     Engraving  metals. 


Appendix.  379 

1863.  April  21.     No.    986.      H.    Rafter.      Obtaining  printing  sur- 

faces. 
,,        April  27.     No.    1,048.     J.   J.    Robert.      Coating  spoons  and 

forks  with  silver. 
„        June   24.      No.    1,595-      T.    Skinner.       Ornamenting  plated 

articles. 
,,        August  22.     No.  2,088.     S.  Moore.     Improved  apparatus  for 

electro-plating. 

1864.  February  29.     No.  497.     F.Weil.     Coating  metals  in  alkaline 

solutions. 
,,        August  15.     No.  2,029.     S.Moore.    Electro-gilding  in  cyanide 

solutions. 
,,         December  14.     No.   3,095.      J.  B.  Thompson.      Coating  iron 

with  palladium,  platinum,  gold,  and  silver. 
,,         December  21.     No.    3,164.      H.   A.    de  Brion.      Varnish  for 

electro-plated  articles. 

1865.  March  10.     No.   677.     T.   Reissig.      Electrolysis  with  photo- 

graphy. 

,,  May  27.  No.  1,457-  R-  A.  Brooman.  Producing  copies  of 
writings,  &c. 

,,  June5.  No.  1,541.  W.  E.Newton.  'Photo-electro-typing 
process.' 

,,        July  6.     No.  1,791.    J.  W.  Swan.    Producing  printing  surfaces. 

,,  August  15.  No.  2,110.  M.  Henry.  Electro-type  with  photo- 
graphy. 

„  October  2.  No.  2,521.  T.Allan.  Preparing  iron  for  electro- 
plating. 

„  October  7.  No.  2,592.  J.  B.  Thompson.  Depositing  iron, 
and  coating  iron  with  platinum,  gold,  silver,  and  copper. 

,,  October  26.  No.  2,762.  H.  Wilde.  Apparatus  for  electro- 
coating. 

,,  November  16.  No.  2,948.  De  la  Haye.  Gilding  copper 
wires  of  telegraphs. 

„        December  23.     No.  3,323.     E.  Clifton.     Electro-bronzing. 

„  December  26.  No.  3,339.  W.F.,Deane.  Coating  the  bottoms 
of  ships  with  copper. 

1866.  February  14.     No.  469.     M.   Henry.     Electro-deposition  with 

photography. 

,,  April  27.  No.  1,186.  M.  Nelson.  Making  moulds  for  electro- 
type plates. 

„  April  27.  No.  1,195.  J.B.Thompson.  Protecting  iron  ships 
from  corrosion. 


380  Appendix. 

1866.  May  8.     No.   1,315.     W.  B.  Woodbury.     Producing  designs 

upon  wood  and  other  substances. 

,,  July  25.  No.  1,934.  C.  E.  Brooman.  Coating  armour-plates 
with  copper. 

„  August  15.  No.  2,095.  J-  Webster.  Coating  metals,  and 
recovering  metals  from  solutions. 

,,  September  28.  No.  2,513.  W.  Clark.  Re-producing  tele- 
graphic signs  and  characters. 

„  November  20.  No.  •  3,047.  C.  E.  Brooman.  Coating  iron 
and  steel,  with  copper  and  its  alloys. 

,,  November  26.  No.  3,113.  R.  H.  Court enay.  Preparing 
printing  surfaces. 

,,        December  u.     No.  3,517.     A.  M.  Clark.     Reduction  of  tin. 

1867.  No.  810.     G.  Bischof.     Coating  metals. 

,,  April  i.  No.  968.  C.  E.  Brooman.  Producing  surfaces  in 
relief. 

1868.  May  29.     No.  1,777.     G.  T.  Bousfield.     Plating  spoons,  &c. 
,,        August  14.     No.  2,545.     J.  B.Thompson.     Preparing  surfaces 

for  gilding,  &c. 

,,  October  10.  No.  3,117.  W.  R.  Lake.  Deposition  of  nickel. 
,,  October  15.  No.  3,155.  H.  A.  Bonneville.  Elastic  moulds. 
„  December  15.  No.  3,801.  A.  Watt.  Making  printing  rollers. 
,,  December  24.  No.  3,930.  W.  H.  Walenn.  Depositing 

copper  and  brass. 

1869.  May  12.     No.  1,458.     P.  W.  Flower  and  H.  Nash.     Coating 

sheets  of  metal. 
,,        July  26.     No.  2,268.      W.  E.  Tilley.      Coating  metals  with 

tin. 
,,        August  17.      No.   2,456.      M.   H.  Jacobi.      Depositing  iron. 

Forming  engraved  surfaces,  &c. 
,,        October  6.     No.   2,961.     B.  Hunt.     Ornamenting  metals  in 

relief. 

„  October  28.  No.  3,125.  W.Brookes.  Deposition  of  nickel. 
„  October  30.  No.  3,159.  A.  Minton.  Coating  iron  and  other 

metals. 
,,        November  23.     No.  3,377.      H.   A.   Bonneville.      Apparatus 

for  keeping  electrolytes  in  motion. 
,,        December  16.     No.   3,643.     A.   Buirat.     Producing  engraved 

plates. 

1870.  February  2.     No.  303.     I.  Adams,  jun.     Deposition  of  nickel. 
,,        February  24.     No.  554.     J.   B.  Elkington  and  C.  E.  Ryder. 

Making  copper  tubes  and  rollers. 


Appendix.  381 

1870.  April  12.     No.  1, 068.     I.  Adams,  jun.     Preparing  surfaces  for 

receiving  nickel  coating. 
,,        August  27.     No.  2,359.     W.  R.  Lake.    Coating  tin-tacks  with 

copper. 

,,        September  28.     No.  2,580.    J.  E.  Bingham.    Deposition  of  tin, 
,,        November  1 6.       No.  3, 005.     G.  Haseltine.     Coating  iron  with 

gold  and  silver. 
,,        December  30.     No.  3,396.     E.  D.  Nagel.     Coating  iron  and 

steel  with  nickel  and  cobalt. 

1871.  June  8.     No.   1,511.     H.  Wilde.      Coating  iron  boilers  with 

copper. 
,,        June  21.      No.    1,626.      J.  Unwin.     Deposition  of  nickel  by 

magneto-electricity.     Nickel  solution. 
,,        July  7.     No.    1,777.     J-   Brough  and  G.  Fletcher.      Coating 

vacuum  pans. 
,,        August  29.      No.  2,266.      T.    Fearn.      Depositing  alloys  of 

nic/cel  and  iron.     Solutions  for  ditto. 
„        September  16.     No.  2,450.     W.  H.  Maitland.     Deposition  of 

copper. 

,,        October  4.     No.  2,623.     De  Lobstein.     Electro-plating. 
,,        December  21.     No.  3,459.     J.   Unwin.     Coating  with  nickel 

by  immersion.     Solution  for  ditto. 

1872.  May  6.     No.    1,376.     Fitzgerald  and  Molloy.     Decomposing 

substances  with  electrodes  of  carbon. 
,,        June  10.     No.  1,742.     C.  A.  Faure.     Manufacture  of  alkalies 

by  electrolysis. 
,,        November   I.      J.    A    Jeancon.      Deposition  of  aluminium, 

(N.B.  American  patent.) 
,,        December  5.     No.  3,680.     T.   Petitjean.      Making  and  orna«- 

menting  articles.     Coating  glass,  &c. 
,,        December  1 8.     No.  3,839      J.  Noad.     Making  moulds  of  sul> 

phide  of  lead,  &c. ,  for  electrotype. 
,,        December  31.     No.  3,970.     J.H.Johnson.    Coating  iron  with 

copper  and  its  alloys. 
,,        No.  95,593.     Mr.  Unwin.    Deposition  of  nickel.    (N.B.  Frencrj 

patent. ) 

1873.  February  10.     No.  474.     R.  Werdermann.     Reducing  rnetah 

from  their  ores. 

,,        No.  476.     R.  Werdermann.     Reducing  metals  from  their  ores 
,,        April  7.     T.  Fearn.     Deposition  of  tin. 

,,        April  29.     J.  T.  Sprague.     Galvanometer  for  use  in  electrolysis. 
,,        July  2.     WT.  R.  Lake.     Coating  iron  with  nickel. 


382  Appendix. 

1873.  December  27.     No.  148,459.     W.  C.  Holman.    Apparatus  to 

show  weight  of  metal  deposited.     (N.B.  American  patent.) 

1874.  No.  1,492.     Brook,   Draper,  and  Unwin.     Preparing  articles 

for  coatings  of  nickel  and  other  metals. 

,,         No.  1,493.     W.  Baker  and  J.  Unwin.     Deposition  of  nickel. 
„         No.  3,033.     J.  B.  Thompson.     Coating  iron  with  gold,  silver, 

and  alloys. 
,,         No.  3,148.     W.   Morgan  Brown.     Preparing  china  and  glass 

for  being  coated. 

,,         No.  3,432.     T.  S.  Johnson.     Producing  electro-type  plates. 
,,         April   19.      E.    Casselbury.      Electrolytic  apparatus.      (N.B. 

American  patent.) 

1875.  No.  58.     Wollaston.     Thermo-electric  apparatus  for  coating 

metals. 

,,         No.  175.     Vera.     Decomposing  water. 
,,         No.  473.     Clark.     Obtaining  metals  from  their  salts. 
,,         No.  519.     Terrell.     Electro-typing  iron  plates. 
„         No.   714.      Brown.      Producing   copper  plates   and  printing 

surfaces. 

,,         No.  1,746.     Bartlett  and  Murray.     Facing  type  with  nickel. 
,,         No.  2,996.     Kilner.     Magneto-apparatus  for  electro-coating. 
,,         No.  3,243.     Alexander.     Electro-typing. 
,,         No.  3,440.     Jewitt.     Making  gas-burners  by  deposition. 
,,         No.  3,904.     Mori.     Thermo-regulators  for  electro-gilding. 
„         No.  4,302.     Blewitt.     Electro-deposition  of  tin. 
,,         No.  4,326.      Ellerbeck   and   Syers.      Making  hydrogen  and 

oxygen. 
„         No.    4,515.      H.    Wilde.      Refining  copper,    and  coppering 

calico-printers'  rollers. 

1876.  No.  1,445.     Werdermann.     Converting  metallic  salts. 

,,  No.  1,704.  Fixsen.     Compound  for  galvano-plastic  uses. 

,,  No.  2,500.  Lake.     Making  wax  moulds. 

„  No.  2,554.  Prior.     Electro-plating  with  nickel. 

,,  No.  2,821.  Zanni.     Magneto-machine  for  plating. 

,,  No.  2,938.  Lake.     Galvanic  battery  for  plating. 

,,  No.  3,181.  Pitt.      Making  copper  tubes,  wire,  &c. 

„  No.  3,515.  Gardner.     Reducing  and  purifying  metals. 

„  No.  3,569.  H.Wilde.     Electro-coppering  rollers. 

,,  No.  3,670.  Faure.     Thermo-battery  for  coating  metals. 

„  No.  4,280.  Haddan.     Magneto-machine  for  plating. 

„  No.  4,302.  R.  J.  Blewitt.     Coating  iron  with  tin. 

„  No.  4,515.  H.    Wilde.      Making    metal    rollers.      Refining 
copper. 


Appendix.  383 

1877.  No.  329.     Drummond.     Producing  printing  surfaces. 

,,  No.  828.     Dodd.     Electro-plating  iron,  copper,  and  nickel. 

„  No.  853.     Parkes.     Separating  nickel  from  copper  in  alloys. 

„  No.  1,023.     Hughes.     Electro-plating  coils  of  wire, 

,,  No.  1,259.     Wiley.     Nickel-plating. 

,,  No.  1,548.     Unwin.     Electro-solution  of  nickel. 

,,  No.  1,572.    Dupuis  and  Schultz.     Gilding  non-metallic  frames. 

,,  No.  2,996.     Kagenbusch  and  Kerr.     Extracting  metals  from 

slags. 

,,  No.  3,476.     Lake.     Electro-tinning  iron  plates. 

,,  No.  3,743.    Johnson.    Magneto-machine  for  electro-metallurgy. 

„  No.  4,053.     Lake.     Magneto-machine  for  electro-plating. 

,,  No.  4,708.     Lake.     Magneto-machine  for  electro-typing. 

„  No.  4,748.     Conradi.     Electro  metallurgy. 

1878.  No.  288.    Johnson.     Nickel-plating  iron  wire. 

„         No.  380.     Van  Winkle.     Nickel-plating  iron  wire. 

,,         No.  1,054.     Parry.     Solution  for  electro-tinning. 

,,  No.  1,228.  Wilde.  Generating  electric  currents  for  use  in 
deposition. 

,,         No.  1,979.     Michaud.     Electro-plating  with  copper. 

,,         No.  2,003.     Hacldan.     Machine  for  electro-plating. 

,,         No.  2,017.     Keith.  Refining  lead  and  separating  gold  and  silver. 

,,         No.  2,407.     Lake.     Making  combs  by  electro- deposition. 

,,         No.   3,392.   Maxwell  Lyte.  Coating  iron  with  copper  and  nick  el. 

„         No.   3,425.  Maxwell  Lyte.  Coating  iron  with  copper  and  nickel. 

,,  '  No.  3,606.     Alexander.     Etching  plates. 

,,         No.  3,976.     Ward.     Magneto-machine  for  plating. 

,,         No.  4,074.     Arnaud.     Dividing  electric  currents  in  plating. 

,,         No.  4,075.     Johnson.     Voltaic  battery  for  electro-plating. 

,,         No.  4,206.     Higgs.     Magneto-machine  for  depositing  metals. 

,,  No.  4,313.  Cochrane.  Generating  electricity  for  electro- 
plating. 

„         No.  4,573.     Zanni.     Machine  for  regulating  electric  currents. 

„  No.  4,6 1 1.  Edwards  and  Normandy.  Generating  electricity 
for  electro-plating. 

„         No.  4,755.     Ccbley.     Precipitating  copper. 

,,         No.  4,921.     Lake.     Solution  for  depositing  nickel. 

,,         No.  5, 127.     Glaser.     Plating  with  nickel  and  cobalt. 

,,         No.  5,250.     Scott.     Thermo-pile  for  depositing  metals. 

1879.  No.  307.      Elphinstone  and  Vincent.      Dynamo-machine  for 

plating. 

,,         No.  359.     Brittain.     Compound  deposit  for  electro -metallurgy. 
,,         No.  529.     Blake.     Electro-depositing  white  metal. 


Appendix. 


1879. 


1880. 


No.  696.     Desmurs.     Producing  designs  on  metals. 

No.  1,203.     Clowes  and  Batey.      Machine  for  black -leading 
moulds. 

No.  1,387.     Lake.     Dynamo-machines  for  plating. 

No.  1,481.     Muller  and  Geisenberger.     Making  saltpetre. 

No.  1,592.     Muller  and  Geisenberger.     Obtaining  ammonia. 

No.  1,692.      Sellon  and  Edmunds.     Regulating  currents  from 
dynamo-machines  for  plating. 

No.  2,821.     Zanni.     Closing  and  opening  circuits  during  de- 
position. 

No.  3,565. 

No.  3,586. 

No.  4,087. 

No.  4,100. 

No.  4,295. 

No.  4,821. 

No.    4,862. 
nickel. 

No.   4,879. 
iron. 

No.  5.030. 

No.  5,085. 

No.  5,175. 


Elmore.     Dynamo-machine  for  plating,  &c. 
Lambotte-Doucet.     Obtaining  metals  from  ores. 
Johnson.     Obtaining  aluminium  and  magnesium. 
Lake.     Dynamo  and  batteries  for  plating. 
Desmurs.     Depositing  metals  for  ornament. 
Elmore.     Nickel  alloys  for  electro-coating. 
Pitt.      Coating  insides  of  provision  cans  with 

Gutensohn.      Separating  tin  from  waste  tinned 


Morgan.     Producing  alkalies  and  salts. 

Wise.     Dynamo-machine  for  plating. 

Joel.     Magneto-machine  for  plating. 
No.  458.     Lake.     Extracting  metals  from  ores. 
No.  830.     Von  Buch.     Depositing  crystalline  carbon. 


No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 


No.   2,020. 

No.  2,465. 

tion. 

No.  2,519. 
No.  2,631. 
No.  2,966. 
No.  3,043. 


,120.     Parry  and  Cobley.     Coating  iron  and  zinc. 

,178.     Perry.     Dynamo-machine  for  plating. 

392.     Lake.  Dynamo-machine  for  plating,  with  regulator. 

,556.     Wirth.     Electro-plating  wood  carvings. 

,570.     Fischer.     Electro-typing. 

,700.     Young.     Producing  ammonia. 

705.     Davies.      Solution  for  depositing  aluminium. 

,909.     Sachs.     Etching  rollers  for  printing. 

Abel.     Separating  substances  by  electrolysis. 

Wetter.     Benzoic  acid  used  in  nickel-plating  solu- 


Barlow.  Electro-typing  inlaid  metal  articles. 

Hodge.  Decomposing  substances  by  electrolysis. 

Sachs.  Producing  designs  on  printing  rollers. 

Glaser.  Electro-plating  with  copper,  nickel,  and 
their  alloys. 

No.  4,005.     Brewer.  Dynamo-machine  for  electro-deposition. 

No.  4,094.     Elmore.  Extracting  copper  and  zinc  from  liquors. 


Appendix. 


335 


1880.     No.    4,541.       Barlow.       Producing   hydrogen   in   alcohol   by 

electrolysis. 
,,         No.  4,985.     Morgan.     Making  alkalies  by  electrolysis. 

1882.  No.  6.     Chaster.     Nickel-plating. 
,,         No.  358.     Moss.     Electro-typing. 

,,         No.  1,639.    Walenn.     Deposition  of  copper,  brass,  and  bronze. 

,,         No.  1,884.     Lake.     Separating  metals  from  their  ores. 

,,         No.  2,875.      Giilcher.      Producing  hydrogen  and  oxygen  by 

gas  batteries. 

,,         No.  3,046.     Barker.  Extracting  geld  and  silver  from  their  ores. 
,,         No.  4,580.     Lake.     Decomposing  alloys  by  electrolysis. 
,,         No.  5,300.     Boult.     Electro-plating  with  nickel  and  cobalt. 
„         No.  5,719.    Appleton  and  Horsfield.     Nickel-plating  engraved 

rollers. 

1883.  No.  88.     Appleton.     Electro-plating  metal  printing  rollers. 
,,         No.  543.     Appleton.     Electro-plating  metal  printing  plates. 
,,         No.  2,281.     Clark.     Depolarising  electrolytes. 

,,         No.  2,577.     Hammersley.     Electro-gilding  vulcanite. 


Table  of  useful  Numerical  Data. 


centimetre 
decimetre 
metre     . 
gramme . 
kilogramme 


ounce  avoirdupois 
pound         , , 
pennyweight  troy 
ounce  troy 
pound    , , 
litre  of  water  . 


gallon  of  water 

J>  5>  • 

cubic  inch  of  water  . 
ounce  measure 
pint  (or  20  ounces)  . 
gallon  (or  160  ounces) 
litre 


"3937  inches. 
3 '937 
39-37 

I5'432  grains. 
I5432- 

3  5  *2  74  ounces  avoirdupois. 
2-2046  pounds         ,, 
437 '5  grains. 
7000- 

24- 
480- 
5760- 
I5432- 
looo*  grammes. 
35'275  ounces  by  measure. 

4-536  litres. 
70000-  grains. 
252-5     „ 

1-733  cubic  inches. 


277-276   ,, 

6i  -024    „ 
C  C 


386 


Appendix. 


At  the  ordinary  temperature  and  pressure  of  the  atmosphere,  100 
cubic  inches  of — 


Hydrogen    . 

Ammonia 

Hydrocyanic 

vapour 
Nitrogen 
Atmospheric  air 


acid 


Grains 

weigh    2  1 1 
„       18-00 

„       28-57 
,,      29-70 


Grains 
Oxygen  .         .         .  weigh  33-80 

Carbonic  anhydride .  ,,  46*50 
Sulphurous  anhydride  ,,  67-78 
Chlorine.          .          .  ,,  76-40 
Sulphuretted  hydro- 
gen     .         .         .  ,,  80-50 


Table  of  Corresponding  Temperatures  on  the  Scales  of 
Centigrade  and  Fahrenheit  Thermometers. 


Deg.  Cent. 

Deg.  Fahr. 

Deg.  Cent. 

Deg.  Fahr. 

Deg.  Cent. 

Deg.  Fahr. 

100 

212 

66 

150-8 

32 

89-6 

99 

2IO-2 

65 

149 

31 

87-8 

98 

208-4 

64 

I47-2 

30 

86 

97 

206-6 

63 

145  '4 

29 

84-2 

96 

204-8 

62 

I43-6 

28 

82-4 

95 

203 

6l 

141-8 

27 

80-6 

94 

201'2 

60 

140 

26 

78-8 

93 

199-4 

59 

138-2 

25 

77 

92 

197-6 

58 

136-4 

24 

75'2 

91 

195-8 

57 

134-6 

23 

73-4 

90 

194 

56 

132-8 

22 

71-6 

89 

I92-2 

55 

131 

21 

69-8 

88 

I90-4 

54 

129-2 

20 

68 

87 

188-6 

53 

127-4 

19 

66-2 

86 

186-8 

52 

125-6 

18 

64-4 

85 

I85 

5i 

123-8 

17 

62-6 

84 

I83-2 

50 

122 

16 

608 

83 

lSl'4 

49 

120-2 

15 

59 

82 

I79-6 

48 

II8-4 

H 

57'2 

81 

177-8 

47 

II6-6 

13 

55'4 

80 

I76 

46 

II4-8 

12 

53-6 

79 

174-2 

45 

"3 

II 

51-8 

78 

I72-4 

44 

I  II  -2 

10 

50 

77 

I70-6 

43 

109-4 

9 

48-2 

76 

I68'8 

42 

I07-6 

8 

46-4 

75 

167 

4i 

105-8 

7 

44"6 

74 

165-2 

40 

IO4 

6 

42-8 

73 

163-4 

39 

102-2 

5 

4i 

72 

l6l-6 

38 

100-4 

4 

39-2 

7i 

70 

159-8 
I58 

37 
36 

98-6 
96-8 

3 

2 

37  '4 
35-6 

69 

156-2 

35 

95 

I 

33'8 

68 

I54-4 

34 

93-2 

O 

32 

67 

I52-6 

33 

91-4 

Appendix.  387 


NOMENCLATURE   OF   ELECTRICAL  UNITS. 

Since  the  publication  of  this  book,  a  revision  has  been  made  of  the 
Nomenclature  of  Electrical  Units. 

The  Unit  of  Resistance  is*  still  termed  an  Ohm,  and  is  equal  to  that 
offered  by  I  '0486  metre  length  of  mercury  of  one  square  millimetre 
section  at  O°  C.  The  amount  of  resistance  in  a  wire,  A,  is  conveniently 
measured  by  dividing  a  current  from  a  very  small  Daniells'  cell,  so  that 
one  portion  passes  through  A  and  one  wire,  B,  of  a  differential  galvano- 
meter, and  the  other  portion  through  another  wire  of  known  resistance, 
c,  and  the  other  wire,  D,  of  the  galvanometer  in  the  opposite  direction 
to  that  through  B,  and  then  the  length  of  A  (or  of  c)  altered  until  the 
needles  of  the  instrument  stay  at  zero ;  the  resistances  of  A  and  c  are 
then  equal.  The  measurement  of  the  degree  of  resistance  of  an 
electrolyte  is  much  more  difficult,  on  account  of  the  varying  polarisation 
of  the  electrodes.  It  may  be  effected  in  a  similar  manner,  by  making 
two  measurements  by  means  of  a  very  feeble  current  after  the  polarisa- 
tion has  become  steady  :  one  when  the  electrodes  are  near  together, 
and  the  other  when  they  are  far  asunder,  using  in  each  case  electrodes 
as  large  as  the  transverse  section  of  the  electrolyte,  and  usually  of  the 
same  metal  as  that  of  the  salt  of  the  liquid.  The  difference  of  resistance 
in  the  two  measurements  is  the  amount  of  resistance  of  the  difference 
of  length  of  the  liquid  in  the  two  cases. 

The  Unit  of  Electro-motive  Force  still  retains  its  name  of  a  Volt. 
That  of  a  Daniells'  cell  is  equal  to  I  -070  volt ;  and  that  of  a  Clarks' 
standard  cell  is  equal  to  1-457  volt.  For  measuring  feeble  electro- 
motive forces,  I  have  devised  a  convenient  form  of  thermo-electric 
pile,  consisting  of  about  300  pairs  of  iron  and  German-silver  wires,  and 
have  employed  it  in  making  a  large  number  of  measurements  not 
much  exceeding  that  of  one  Daniell.  It  is  capable  of  measuring 
differences  of  ^5  of  a  volt  (see  '  Proceedings  of  the  Birmingham 
Philosophical  Society,'  vol.  iv.  Part  i). 

The  Unit  of  Strength  of  current  is  now  termed  an  Ampere,  and  is 
the  strength  produced  by  an  electro-motive  force  of  one  volt  in  a 
circuit,  having  a  resistance  of  one  ohm  ;  it  was  formerly  termed  '  one 
Weber  per  second.'  It  is  that  current  which  will  deposit  in  a  solution 
of  argento-potassic  cyanide,  containing  the  least  practical  amount  of 
free  cyanide  of  potassium,  '017343  grain  of  silver  per  second  ;  or  will 
liberate  from  dilute  sulphuric  acid  with  platinum  electrodes,  -000162 

c  c  2 


388  Appendix. 

grain  of  hydrogen  per  second;  or  will  deposit  '0051035  grain  of 
copper  per  second  from  the  usual  sulphate  solution. 

The  Unit  of  Quantity  of  current  is  now  termed  a  Coulomb  (formerly 
a  Weber).  It  is  but  little  used  ;  and  is  the  amount  which  one  Ampere 
gives  in  one  second. 

An  Unit  of  Density  of  current  would  be  of  great  value  in  electrolysis, 
but  one  has  not  yet  been  adopted.  I  have  suggested  that  of  one  Ampere 
leaving  or  entering  one  square  centimetre  of  surface  of  electrode  per 
second  (see  'Proceedings  of  the  Birmingham  Philosophical  Society,'  vol. 
iii.  p.  277). 


INDEX. 


ACK 
ACETATES  of  copper  and  lead,  364, 

Acid,  acetic,  electrolysis  of,  29 

—  arsenious,  357 

—  benzoic,  electrolysis  of,  96 

—  stains,  removing  of,  367 

Acids,   electric  relations  of   metals  in, 
table  of,  63 

—  electrolysis  of,  96,  115,  117,  120,  125, 
126,  150,  256,  311 

—  first  decomposed,  2 

—  for  batteries,  330 

—  for  cleaning    rticles,  318 
Alkalies,  electric  relations  of  metals  in 

table  of,  65 

—  for  cleaning  articles,  317 
Alkali-metals,  deposition  of,  5,  295 

—  discovery  of,  3 

Alkaline-earth    metals,     deposition    of 

286 

Alloys,  deposition  of,  50,  272,  278 
Aluminium,  deposition  of,  289 
Amalgam  of  gold,  358 
Ammonia,  360 

—  electrolysis  of,  312 

—  gas,  preparation  of,  360 
Ammonium,  deposition  of,  305 
— -  carbonate  of,  361 

Analysis  of  brass  by  electrolysis,  285 

—  copper  ores  by  electrolysis,  213 

—  cyanide  of  potassium,  363 

—  dirt  from  copper  anodes,  210 

—  silver-plating  solution,  175,  184,  186, 

A1'87 

Anions,  34 
Anode,  33 

—  of  scraps  of  metal,  239,  343 
Antimony,  deposition  of,  77,  81,  84,  88, 

99 

—  electro-deposited,  properties  of,  103 

—  selection  of,  357 
Antique  silver,  181 
Aqua-fords,  354 

—  dipping  liquid,  320 
Aqua-regia,  355 


BOO 

Arbor  Dianse,  i 
Argentic  cyanide,  148 
Argentic  chloride  and  nitrate,  358 
Arsenic,  97 

—  in  copper,  31 

—  testing  for,  98 

—  white,  357 
Arsenious  acid,  357 
Atomic  weights,  table  of,  42 


r>  ARIUM,  deposition  of,  295 

•^     Base  metals,  deposition  of,  198 

gilding,  137,  142,  143 

for  electro-plating,  preparation  of, 

162 
Batteries,  exciting  liquids  for,  330 

—  how  managed,  335 

—  of  two  metals  in  one  liquid,  67 

—  of  two  metals  in  two  liquids,  69 

—  relative  power  of,  329 
Battery  cells,  334 

—  liquids,  330 

—  plates,  size  of,  its  effect  upon  the  cur- 
rent, 4 

—  process    for    making     silver-plating 
liquid,  165 

—  process,  separate,  23,  89 

—  power,  how  regulated,  337 

—  relation  of  action  in,  to  that  in  depo- 
siting vessel,  74 

Benzoic  acid,  electrolysis  of,  96 
Berzelius  notices  electrolytic  transfer,  3 
Binding  screws,  334 
Bismuth.  357 

—  deposition  of,  77,  82,  85,  in 
Bisulphide  of  carbon,  356 

in  bright  plating,  26,  167 

Black  cyanide,  362 

—  lead,  gilding,  217 
objects.  216 

process  first  used,  23 

Blue  vitriol,  358 

Books  on  electro-deposition,  369 


390 


Index. 


BOR 

Boron,  depositions  of,  308 

Brass,  analysis  of  by  electrolysis,  285 

• —  deposition  of,  278 

—  first  deposited,  25 

—  stripping  silver  from,  183 
Brassing,  solution  for,  282 
Bright  silver-plating,  26,  167 

Brittle    negative    metals,  deposition  of, 

97 

Bromine,  deposition  of,  311 
Bronze,  deposition  of,  272 

—  powder,  to  render  surfaces  conductive, 
217 

Brugnatelli  discovers  electro-gilding,  3 

—  discovers  solution  of  the  anode,  3 
Brunei's  brassing  solution,  279 
Bunsen's  battery,  328 

Busts  copied  in  copper,  227 

—  moulding  of,  228 


/CADMIUM,  deposition  of,  273 
**•'     —  salts  of.  273 
Caesium,  deposition  of,  305 
Calcium   deposition  of,  292 

—  salts  of,  292 

Calico-printing  rollers  produced  by  de- 

sition,  205,  349 
Carbon,  bisulphide  of,  356 

—  deposition  of,  309 
Carbonate  of  ammonium,  361 

—  lead,  359 

—  potassium,  360 

—  sodium,  360 

Carlisle  and  Nicholson  decompose  water, 

2 

Cathode,  34 
Cations,  34 
Caustic  lime,  359  M 

—  potash,  360 

for  cleaning  articles,  317 

—  solution,  preparation  of,  360 

—  soda  electrolysed,  151,  297 
Cells,  battery,  334 

—  number  of,   its  influence    upon  the 
electric  current,  4,  74 

Cement  for  lining  depositing  vats,  315 
Cerium,  deposition  of,  288 
Chemicp-electric  action,  28 

—  relations  of  substances,  61 
Chloride,  argentic,  358 

—  of  gold  and  of  platinum,  357 

—  of  silver,  testing,  358 

—  of  tin,  359 

Chlorides  decomposed  before  oxides,  3x1 
Chlorine,  deposition  of,  311 
Chromium,  deposition  of,  252 
Clamond's  thermo-electric  pile,  353 
Clay  figures  coppered,  222 
Cleansing  metals   to  receive   a  deposit, 
3'5,  319 

—  silvei,  182 

Cloth  coated  with  copper,  216 
Cobalt,  deposition  of,  241 


GRIT 

Coins  copied  in  copper,  224 

—  copied  in  plaster  of  Paris,  226 

—  moulding  of,  224 

Coke  as  a  substitute  for  zinc  in  batteries, 

68 

Coloured  gilding,  138 
Composition  for  moulding,  225 

—  of  electro-deposited  antimony,  107 
Compound  cell  apparatus,  34 
Conducting  powers  affected  by  tempera- 
ture and  purity,  31 

of  bodies  generally,  28 

of  metals,  30 

—  wires,  effect  of  dimensions  of,  32 
Conduction,     resistance     to,     generates 

heat,  31,  32 

Conductors  and  non-conductors  of  elec- 
tricity, 29 

Copper,  acetate  of,  364 

—  arsenic  in,  31 

—  conductivity  of,   affected  by  arsenic 
and  iron,  31 

—  cost  of  depositing,  210 

—  deposition  of,  78,  82,  86,  88,  198 
application  of,  202 

by  means  of  silicon,  200 

prevented  from  adhering,  214 

upon  non-metallic  surfaces,  216 

—  electric  relations  of,  199 

—  estimation  of,  213 

—  extracted  from  mineral  liquids,  203 

—  large  objects  copied  in,  229 

—  ores,  analysis  of,  by  electrolysis,  213 

—  plates  coated  with  iron,  246 
etched,  231 

—  purity  of,  its  influence  on  electric  con- 
ductivity, 31 

—  pyrites,  their  treatment,  203 

—  rapidity  of  deposition  of,  210 

—  refined  by  electrolysis,  212 

—  removal  from  silver  articles,  184 

—  separated  from  zinc  by  electrolysis,  285 

—  solutions,  207,  247 

cyanide  of,  207 

management  of,  209 

—  sulphate  of,  358 

Coppering  articles  of  cast  iron,  203-221 

—  cloth,  216 

—  human  corpses,  222 

—  metals  generally,  206 

—  plaster  and  clay  figures,  222 

—  porcelain  and  glass,  232 

—  fruit,  flowers,  &c.,  221 

—  zinc  and  iron,  208 

Copying  busts  and  statues  in  copper,  227 
-  —  coins  and  medals  in  copper,  224 

—  Daguerrotype  plates  in  copper,  215 

—  engraved  plates  in  copper,  214 

—  set-up  type  in  copper.  223 

—  wood  engravings  in  copper,  222 
Corpses  coated  with  metals,  222 
Cream-jugs,  how  gilded,  143 
Crown  of  cups,  Voita's,  2 

Crude  copper  by  electrodes,  purification 
of,  212 


Index. 


391 


CRU 

Cruickshank,  noticed  electro-deposition 
of  metals,  3 

—  his  trough  battery,  2 
Crystals  of  deposited  metals,  39 

—  —  tin,  269 
Cupric  sulphate,  358 

Cupriferous  mineral  liquids,  how  treated, 

203 
Current,  density  of,  affects  the  deposit, 

38, 

—  electric,  71 

—  measurement  of,  72 

—  strength  of,  70 
Cyanide,  argentic,  148 

—  black,  362 

—  of  copper  solutions,  207 

—  of  gold,  124 

—  of  mercury,  195 

—  of  potassium,  361 

analysis  of,  363 

impurities  in,  364 

preparation  of,  363 

—  of  silver,  148 
Cyanides  first  employed,  19 

—  patented    by     Elkington    and     De 
Ruolz,  21 

Cylinders  of  iron  coated  with  copper, 
205,  349 

T^AGUERREOTYPE  plates  copied, 

Dancing  and  singing  mercury,  197 
Daniell's  battery,  327 
Davy  deposits  sodium  and  potassium, 
297,  299 

—  discovers  the  alkali  metals,  3 
Dead  gilding,  138 

—  silvering,  180 

Debris  from  copper  anodes,  210 
Definite  electro-chemical  action,  4,  44 
De  la  Rive,   his  early  experiments   in 

gilding,  23 
De  la  Rue.  his  observation  with  a  Daniell's 

cell,  4 
De  Ruolz,  first  deposits  brass,  25 

—  his   French  patent  for  the  cyanides, 
21 

Density  of  current,  effect  of,  38 
Deposited  metals,  porosity  of,  38 
structure  of,  38 

—  silver,  thickness  of,  178 
Depositing,  by  the  compound  cell  appa- 
ratus, 24 

—  copper  upon  glass  and  porcelain,  232 

—  liquids,  mishaps  in  making  and  using 
them,  341 

accidents      and      mishaps     with, 

—  —  management  of,  92,  341 
selection  of,  340 

strata  and  streams  in,  55 

testing,  341 

—  methods  of.  76 

—  processes,  selection  of,  339 


Depositing  room,  arrangement  of,  314 

—  several  metals  in  succession,  50,  140 
Deposition,  by  metals  in  liquids,  81-87 

—  by  separate  currents,  89 

—  by  simple  immersion,  77 

—  general  methods  of,  76 

—  of  alkali-metals,  295 

—  of  alloys,  50,  272,  278 

—  of  metals,  first  observed,  3 

in  cyanide  solutions,  order  of,  140 

—  of  silver,  remarkable  instance  of,  154 

—  of  tin,  remarkable  instance  of,  265 

—  in  compound  cell  apparatus,  90 

—  regulation  of  the,  35-39,  54-55,  74-75, 
9°-93.  337.  344-347 

—  speed  of,  38,  347 

Deposits,  adhesion  of  prevented,  214 

—  alloy  of,  with  the  cathode,  47 

—  circumstances  which  affect  the  quality 
°f>  35 

—  circumstances  which  affect  the  quan- 
tity of,  39 

—  of  copper  first  observed,  4 

—  regulation  of,  344 
Didymium,  deposition  of,  288 
Diffusion  in  electrolytes,  56 
Dipping  liquids,  318 

Dirt,  analysis  of,  from  copper  anodes, 
210 

—  upon  anodes  of  nickel,  239 
Distilled  water,  354 
Dyads,  41 


T7ARTH   METALS,  286 

•*"*     Elastic  composition,  moulds  of,  227 

—  moulds  patented  by  Dr.  Leeson,  25 
Electrical  units,  nomenclature  of,  387 
Electric  conducting    powers,    table   of, 

29-31 

—  current,  71 

quantity  of,  conditions  of,  4,  72 

regulation  of,  337 

•—  principles  of  electro-metallurgy,  28 

—  relations  of  copper,  199 
of  metals  in  liquids,  62-69 

—  of  metals  in  potassic  cyanide,  65 

—  of  tin  and  iron,  264 
Electricity,  series  of  conductors  and  in- 
sulators of,  29 

Electro-chemical  action,  28,  32 

conditions  of,  32 

definite,  laws  of,  44 

equivalency  of,  42 

equivalents,  determination  of,  44 

of  deposited  antimony,  105 

Electro-chromy,  260 

Electro-deposited  antimony,  composition 
of,  107 

—  properties  of,  103 

bright  silver,  properties  of,  169 

iron,  uses  and  properties  of,  248 

—  nickel,  properties  and  uses  of,  240 
metals,  purity  of,  49 

quality  of,  35 


392 


Index. 


ELE 

Electrodes,  actions  at,  33 

—  meaning  of  the  term,  33 

—  polarisition  of,  54 
Electro-etching,  231 
Electrolysing  liquids,  force  required,  75 
Electrolysis,  binary  theory  of,  45 

—  direction  of,  35 

—  earliest  known  facts  of,  i 

—  localities  of,  32 

—  meaning  of  the  term,  33 

—  nomenclature  of,  33 

—  of  acids,  96,   115,  117,  120,  125,   126, 
150,  256,  311 

—  of  mixed  liquids.  50 

—  phenomena  of,  33,  173,  176 

—  rate  of,  necessary,  36 

—  secondary  effects  of,  46 

—  terms  used  in,  33 

—  theories  of,  45 

Electrolytes,  decomposability  of,  34 

—  diffusion  in,  56 

—  direction  o»  electric  current  in,  35 

—  meaning  of  the  term,  33 

—  movements  in,  ,55 

—  series  of,  in  their  order  of  decompos- 
ability, 34 

Electrolytic  movements,.^ 

—  phenomena,  33,  173,  176 

—  transfer  first  noticed,  3 

—  vibrations  of  mercury,  3,  197 
Electro-metallurgy,  books  on,  369 

—  chemical  principles  of,  60 

—  electric  principles  of,  28 

—  historical  sketch  of  the  subject,  i 

—  laws  and  principles  of,  28 

—  peculiar  phenomena  in,  176,  215 

—  special   information   respecting   sub- 
stances used  in  the  art,  354 

—  technical  section  of  the  subject,  313 

—  theoretical  division  of  the  subject,  28 
Electro-motive  force,  cause  of,  70 

'  Electro-platers  to  the  trade,'  180 
Electro-plating,  early  difficulties  in,  22 
Electro-type,  early  experiments  in,  5 
Elkington's  first  experiments  in  gilding, 
19 

—  patent  for  the  cyanides,  21 

—  process  ,or  refining  copper,  212 
Engraved  plates  copied  in  copper,  214 
Etching  copper  plates,  231 
Explosive  deposits,  48,  103 
External  resistance,  72 


definite 


P  ARAB  AY'S    discovery    of 
•*•       electro  chemical  action,  4 

—  discovery  of  magneto-electricity,  4 

—  theory  of  electrolysis,  45 
Fearn  s  tinning  solution,  270 
Ferrocyanide  of  potassium,  364 
Filters  and  filtration,  365 
Flowers  c  )ated  with  metal,  221 

1 1-ior.c  a  id,   355      ^ee  also   HYDRO- 
FLUORIC ACID 


GRE 

Fluorides  el  ctrolysed,  116,  121,  126,  147, 
150,300.  See  also  HYDROFLUORIC  ACID 

Fluorine,  deposition  of,  311 

Formic  acid,  electrolysis  of,  96 

French  process  of  silver-plating,  166 

Fruit  coated  with  metal,  221 

Fulminating  gold,  123 

Fused  fluoride  of  potassium  electrolysed, 
300 

—  salts,  electrical  relations  of  metals  in, 
66,  67 

employed    for   electro-deposition, 

26,  165 

—  substances,  electric  relations  of  metals 
in,  66 

Fusible  alloy,  moulds  of,  224 


C*  ALLIUM,  deposition  of,  288 
^"^     Galvanometer,  62,  73 
Galvano-plastic  experiments,  5 
Gas-carbons,  328 
Gases,  conduction-resistance  of,  31 

—  relative  weights  of,  table  of,  386 
Gelatine  moulds,  227 
Gerboin's  experiments,  3,  197 
German-silver  deposited,  285 
Gilding  base  metals,  137,  142,  143 

—  black  lead,  217 

—  by  simple  immersion,  128 

—  coloured,  138 

—  correction  of  colour  in,  139 

—  first  experiment,  3 

—  free  cyanide  in,  140 

—  green,  138 

—  hot,  136 

—  insides  of  vessels,  143 

—  metal  dipped  bright,  320 

—  pink,  138 

—  red,  138 

—  solutions,  127,  132 

—  yellow,  138 

Gladstone's  experiments,  37,39,  201 
Glass  coated  with  copper,  232 
Glucinium,  deposition  of,  292 
Glyphography,  Palmer's,  25,  231 
Gold  amalgam,  358 

—  chloride  of,  357 

—  cost  of  depositing,  179 

—  cyanide  of,  124 

—  deposition  of,  39,  77,  122 

—  methods  of  punfyine,  141,  144,  193 

—  ornamentation  on  silver  articles,  181 

—  pink,  138 

—  precipitation  of,  from  cyanide   solu- 
tions, 144 

—  recovery  of,  from  old  solutions,  144, 
187 

—  removal  from  silver  articles,  184 

—  solid  deposition  of,  136 

—  solution,  management  of,  141 
Golding  Bird's  experiments,  5,  308 
Gramme's  magneto-electric  machine,  349 
Graphite,  217,  355 

Grease  stnins,  how  to  remove,  567 


Index. 


393 


GRE 

Greek  fire,  357 

Grotthus's  theory  of  electrolysis,  45 
Grove's  battery,  329 
Guiding-wires,  26,  216 
Gutta-percha  composition,  225,  315 
moulds  of,  2^3 


1 1  EAT,     evolved     by  conduction-re- 
•*•         sistance,  32 

by  explosive  antimony,  103 

in  magneto-electric  machines,  59 

Henderson's     process      for     extracting 

copper,  204 

Henry  decomposes  the  common  acids,  2 
Hexads,  41 

Hisinger  notices  electrolytic  transfer,  3 
Hot  coppering  solution,  207 

—  gilding,  136 
Hydrochloric  acid,  355 

—  electrolysis  of,  95,  117,  125,  311 
Hydroc\anic  acid,  361 
Hydrofluoric  acid,  355 
electrolysed,  96,  115,  120,  126,  150, 

312 
Hydrogen, absorbed  by  deposited  metals, 

96,  240 

—  deposition  of,  94 
Hydrometers,  365 

Hyposulphite  of  silver-plating  solution, 
164 


T  NDIUM,  deposition  of,  262 
•*•     Intensity  of  current,  72 

in  relation  to  number  of  elements,  4 

Internal  resistance,  72 
Iodine:,  deposition  of,  311 
Indium,  deposition  of,  114 
Iron,    absorption   of  hydrogen   by   de- 
posited, 48,  249 

—  coated  with  copper,  207 

—  deposition  of,  79,  82,  243 

—  electric  relations  of,  264 

—  electro-deposited,  properties  and  uses 
of,  248 

—  solution,  management  of,  248 

—  stripy  ing  gold  from,  143 

—  sulphate  of,  359 


T  ACOBI'S  galvano-plastic  experiments, 

Johnson  and  Morris's  solution  for  de- 
positing brass,  281 

—  solution  for  depositing  German- 
silver,  285 

Jones's  patent  for  metallising  non-con- 
ductors, 25 

Jordan's  early  experiments  in  electro- 
type, 5 


T^LEIN'S  process  for  electro-deposit- 
•*-v     ing  iron,  246 


MET 
T  AMP-POSTS  coated    with  copper 

***       221 

Lanthanium,  deposition  of,  288 
Lathe  for  scratch-brushing,  316 
Laws  of  electro-metallurgy,  28 
Lead,  acetate  of,  365 

—  carbonate  of,  359 

—  deposition  of,  79,  83,  257 

—  white,  359 
Leeson's  patent,  25 

Lenoir's    process     of     making     copper 

statues,  230 
Lime,  359 
Liquids,  battery,  330 

—  conduction-resistance  of,  30 

—  depositing,  management  of,  92,  341 
selection  of,  340 

—  dipping,  318 

—  mixed  ones  electrolysed,  51 
Lithium,  deposition  of,  295 
Luckow's  process  of  analysing    copper 

ores,  213 
Lunar  caustic,  358 


]\TAGNESIU^1,  deposition  of,  286 
1¥J-     Magnetorelectric       action,       dis- 
covered, 4 

first  applied  in  metallurgy,  25 

principles  of,  56,  57 

machines,  347 

by  Siemens,  351 

waste  of  power  in,  59.  351 

Manganese,  deposition  of,  249 
Mason's  separate  baUery  process,  23,  89 
Measurement  of  current,  72 
Measures  and  weights,  table  of,  381 
Medallions  copied  in  copper,  214 
Mercurial  electrodes,  sounds  produced 
in,  197 

—  solutions  for  quicking,   143,  166,  196, 
323 

Mercury,  358 

—  agitated  by  electrolysis,  3,  197 

—  cyanide  of,  195 

-   deposition  of,  78,  82    195 

—  first  employed  to  make  silver  deposits 
adhere,  23 

—  recovery   of    from   old    zinc    plates, 

Merrick's  process  of  estimating  copper 

in  its  salts,  213 
Metallic  toys,  covered  with  peroxide  of 

lead,  261 

—  at  Nuremberg,  colouring  of,  261 
Metallising     non-conducting     surfaces, 

217,  247 

Metallo-chromy,  4,  260 
Metalloids,  deposition  of,  307 
Metals,  alkali,  295 

—  amount  of  electricity  produced  by 
74 

— 'base,  198 

—  black  deposits  of,  37 


394 


Index. 


MET 
Metals,  conducting  powers  of,  30 

—  deposited,  cracking  of,  37 
crystals  of,  38,  39,  269 

quantity  of,  conditions  of,  39,  74, 

first  observed,  3 

—  earth,  286 

—  electro-deposited,  purity  of,  49 
quality  of,  35 

—  in  liquids,  electric   relations  of,  62- 
69 

—  negative,  97 

—  noble,  113 

—  silvering    of,   mentioned    by   Pliny, 

Molybdenum,  255 

Molybdic  acid,  electrolysis  of,  256 

Monads,  41 

Morris  and  Johnson's  solution  for  de- 
positing brass,  281 

solution  for  depositing  German- 
silver,  285 

Mother-of-pearl  copied,  27 

Motion,  apparatus  for  keeping  articles 
in,  174 

Moulding  busts  and  statues,  228 

—  coins,  224 

—  composition  for,  225 

Moulds  of  fusible  alloy,  wax,  gutta- 
percha,  224 

—  of  plaster  of  Paris,  and  elastic  com- 
position, 226,  227 

Muriate  of  gold,  357 

—  platinum,  357 

—  silver,  358 

—  ri?«  359 
Muriatic  acid,  355 

Murray  devises  the  process  of  black- 
leading,  23 


T^APIER,  deposits  metals  from  fused 

•^      minerals,  26 

— 's  method  of  analysing  silver-plating 

solutions,  i?7 
Negative  electrode,  33 

—  meaning  of  the  term,  34 

—  metals,  deposition  of,  94 

—  substances  set  free  at  the  anode,  35 
Nicholson  and  Carlisle  decompose  water, 

2 
Nickel,  359 

—  deposition  of,  82,  232 

—  electro-deposited,  properties  and  uses 
of,  240 

—  estimation  of,  233,  240 

—  first  deposited,  21 

—  solution,  management  of,  238 

—  testing,  359 

'  Nielled  silver,'  181 
Nitrate,  argentic,  358 

—  of  silver,  testing,  358 
Nitric  acid,  354 

testins-  3^4 


POS 

Nitric  acid,  electrolysis  cjf,  96,  117 
Nitrogen,  deposition  of,  312 
Nitrp-hydrochlonc  acid,  355 
Nobili's  rings,  4,  260 
Noble  metals,  deposition  of,  113 
Noe's  thermo-electric  pile,  351 
Nomenclature  of  electrolysis,  33 
—  of  electrical  units,  387 
Non-conducting  surfaces,  how  rendered 

conductive,  216 
Numerical  data,  385 


QHM'S  law,  71 
^     Oil  of  vitriol,  356 

for  batteries,  330 

Osmium,  deposition  of,  113 

Oudry's  process  for  coppering  articles  of 

iron,  221 

Oxalic  acid,  electrolysis  of,  96 
Oxides  decomposed  before  fluorides,  311 
Oxidised  silver,  180 


PALLADIUM,  deposition  of,  114 
Palmer's  glyphography,  25,  231 
Pans  for  acid  liquids,  322 
Parkes,  deposits  metals  from  fused  salts, 
26,  165 

—  his  solution  for  solid  silver  deposits, 
161 

Patents,  list  of,   on  electro-metallurgy, 

371 

Pearlash,  360 
Peroxides  formed  upon  anodes,  4,  55, 

150,  151,  242,  252,  260 
Phenomena  of  electrolysis,  33,  176,  215 
Phosphorus,  356 

—  deposition  of,  310 

—  moulding  composition,  219 

—  solution,  218,  247,  357 

first  used  to   render  surfaces   con- 
ductive, 25 
Pink  gold,  138 
— •  silver,  181 
Plaster  of  Paris  figures  coppered,  222 

moulds  of,  226 

Plating  balance,  180 

—  with  silver  in  melted  salts,  165 
Platinic  chloride,  357 
Platinised  silver,  118,  181 

— •  —  its  advantages  in  a  battery,  327 
Platinising,  118,  120 
Platinum,  chloride  of,  357 

—  deposition  of,  118 
Plumbago,  217,  355 

Poisons  and  their  antidotes,  366 
Polarisation  of  electrodes,  54 
Polishing  paste  for  silver  articles,  182 
Porcelain  coated  with  copper,  232 
Porous  cells  for  batteries,  334 
Positive  electrode,  33 

—  meaning  of  the  *erm,  35 

—  substances  set  free  at  cathode,  35 


Index. 


395 


POT 

Potash,  360 

Potassic  cyanide,  electric   relations  of, 

65 
how  made,  361 

—  fluoride  electrolysed,  300 
Potassium,  carbonate  of,  360 

—  cyanide  of,  361 

—  deposition  of,  298 
Potential  and  tension,  71 
Principles  of  electro-metallurgy,  28 
Prussiate  of  potash,  361 

—  —  yellow,  364 
Prussic  acid,  361 
Pyro-plating;  47,  339 


articles    to    receive    a 
Vc     deposit,  323 

—  process  first  employed,  23 

—  solutions,  143,  166,  196,  323 
Quicksilver,  358 


RED-GILDING,  138 
Reguline    state,   meaning   of    the 

term,  36 

Reinsch's  test  for  arsenic,  98 
.Resistance,  intensity  of  current,  72 
Rhodium,  deposition  of,  113 
Roseleur's  solution  for  brassing,  282 
—  coppering,  207 

— tinning,  270 

Rubidium,  deposition  of,  305 
Russell  and  Woolrich's  solution  for  de- 
positing Cadmium,  274 
Ruthenium,  deposition  of,  113 


C  ALTS,   table  of  electric  relations  of 
*^     metals  in,  65 

—  fused,  conductivity  of,  30 

—  of  Tartar,  360 

—  smelling,  361 
Sal  Volatile,  361 

Salzede's  brassing  solution,  279 
Scheele's  prussic  acid,  361 
Schlumberger's    process   for    coppering 

iron  cylinders,  205 
Schottlaender's    process    for    coppering 

cloth,  216 
Scrap  anodes,  343 
Scratch-brushes,  316 
Screws,  binding,  334 
Seebeck  discovers  thermo-electricity,  4 
Selenium,  deposition  of,  310 
Set-up  type  copied  in  copper,  223 
Shore  deposits  nickel,  21 
Siemens's  magneto-electric  machine,  351 
Silicon,  deposition  of,  308 

—  deposits  silver  and  copper,  152,  200 
sodium,  297 

Silliman  copies  mother-of-pearl,  27 


STA 
Silver,  antique,  181 

—  articles,  ornamenting.  181 

—  chloride  of,  358 

—  cost  of  depositing,  179 

—  cyanide  of,  148 

—  deposition  of,  77,  82,  85,  146 
bright,  26,  167 

by  chemical  means,  154 

colour  of,  177 

by  silicon,  152 

re-dissolving  of,  176 

remarkable  instance  of,  154 

upon  cast-iron,  163 

upon  wax  moulds,  218 

upon  soft  solder,  164 

Silver,  electro-deposited,  properties  of, 
169 

—  first  coppered  by  electro-process,  3 

—  its  purity  tested,  104,  357 

—  method  of  purifying,  194 

—  pink,  181 

—  plating,  French  process  of,  166 

in  France,  regulation  of,  179 

liquid,  composition  of,  159 

solution,  analysis  of,  175,  184,  186, 

187 

bright,  preparation  of,  167 

made  by  battery  process,  165 

made  by  chemical  method,  156 

strength  of,  155 

—  sulphite  of,  153,  164 

—  platinised,  118,  181 

—  precipitation   of,   from  cyanide  solu- 
tions, 144 

—  purification  of,  194 

—  d-ppsited,  quality  of,  171 

—  rapidity  of  deposition  of,  178 

—  recovery  of,  from  old  solutions,  187 

—  removal  frorn  copper  articles,  183 

—  solid  deposition  of,  161 

—  solution,  management  of,  172-178 

—  stripping  copper  from,  184 

—  stripping  gold  from,  184 
Silvering  solution,  free  cyanide  in,  140, 

i?5 

—  metals,  mentioned  by  Pliny,  i 
Single  cell  apparatus,  18 
Smee's  battery,  327 

—  experiments     in     electro-deposition, 
25 

'  Smelling  salts,'  361 

Soda,  360 

Sodium,  carbonate  of,  360 

—  deposition  of  by  silicon,  297 
Solid  deposition  of  gold,  136 
of  silver,  161 

Sounds  produced  in  mercurial  electrodes, 
197 

Spencer's  early  experiments  in  electro- 
type, 5 

Spirits  of  hartshorn,  360 

—  of  sal'.s,  355 

Stains,  how  to  remove,  367 
Statues  copied  in  copper,  229 

—  moulding,  228 


396 


Index. 


STE 

Steel  engraved  plates  copied  in  copper, 
214 

—  rendered  brittle  by  absorbed  hydro- 
gen, 49,  97  _ 

Stereotyping  in  copper,  17,  223 
Stopping-off  varnishes,  182,  227,  323 
Strata  in  depositing  solutions,  55,  173 
Streams  in  depositing  solutions,  55 
Stripping  articles,  183 
Strontium,  deposition  of,  294 
Subsalts  in  deposited  silver,  177 
Substances,  resistance  of,  to  the  electric 
current,  30 

—  relative  conducting  powers  of,  29 
Sugar  of  lead,  365 

•Sulphate  of  copper,  depositing  solution, 

206 
testing,  358 

—  of  iron,  359 
Sulphide  of  carbon,  356 

Sulphite  of  silver-plating  solutions,  153, 

164 

Sulphur,  deposition  of,  310 
Sulphuretted  hydrogen  gas,  preparation 

°f>  355 

Sulphuric  acid,  330,  356 
Sulphurous  anhydride  gas,  preparation 

of,  356 
Sulzer  mentions  the  taste  of  lead  with 

silver,  2 
Surfaces,   rendering    them    conductive, 

216 
Syphons,  365 


'pARTARIC    ACID,    electrolysis  of, 

Tellurium,  deposition  of,  98 

Temperature,  influence  of,  upon  conduc- 
tivity, 31 

Temperatures  corresponding,  table  of, 
386 

Tension  and  potential,  71 

Testing  acids  for  batteries,  330 

—  for  arsenic,  0,8 

—  chloride  of  silver,  358 

—  cyanide  of  potassium,  363 

—  depositing  liquid,  341 

—  nickel,  359 

—  nitrate  of  silver,  358 

—  nitric  acid,  354 

—  silver,  194 

—  sulphate  of  copper,  358 

—  tin,  359 
Test  papers,  365 
Tetrads,  41 

Thallium,  deposition  of,  262 
Thermo-electric  action,  59 

—  piles,  351 

—  series,  60 
Thermo-electricity,  discovered,  4 

—  employed  for  deposition,  26 
Thermometers,  365 
Thermometric  scales,  382 


WAX 

Tin,  chloride  of,  359 

—  deposition  of,  79,  83,  88,  263 
crystals  of,  269 

—  —  remarkable  instance  of,  265 

—  electric  relations  of,  264 

—  salt,  359 

—  testing  of,  359 
Tinning,  solution  for,  270 
Titanium,  307 

Transference  by  electrolysis  first  ob- 
served, 3 

Trees  of  lead  and  tin,  how  formed,  257, 
265 

Triads,  41 

Trinkets  for  '  dead  gilding,'  preparation 
of,  139 

Trough,  battery,  Cruickshank's,  2 

Tungsten,  255 

Type  copied  in  copper,  223 


TJRANIUM,  253 


WALENCY  of  elements,  table  of,  41 
*      —  relation  of,  to  electrolysis,  42 
Vanadium,  257 
Varnishes  for   'stopping  off,'  182,   226, 

323 
Vat,  advantages  of  motion  of  articles  in, 

—  silver,  arrangement  of,  169 

—  for  containing  solutions,  169,  315 

—  for  depositing,  cement  for  lining,  315 

—  motion  of  articles  first  adopted  in,  26 

—  motion  of  articles,  how  produced  in, 
I7'>. 1.74 

—  positions  ot  articles  in  plating,  343 
Verdigris ,  364 

Vitriol,  blue,  358 

—  green,  359 

Volta's  great  discovery,  2 

Voltaic  batteries,  management  of,  335 

used  in  electro-metallurgy,  326 

—  currents,  source  of,  70 
Voltameter,  73 

—  first  employed,  4 


VyALENN'S  alkaline  coppering  so- 
*      lution,  208 

—  brassing  solution,  284 

—  process  for  depositing  iron,  245 
Washing  soda,  360 

Wash-waters  treated  for  gold  and  silver, 

144,  187 
Water,  354 

—  first  decomposed  by  electricity,  2 
Watts'  brassing  solution,  281 

—  cvanide  of  copper  solution,  281 

—  process  for  depositing  zinc,  277 
Wax  moulds,  224,  225 


Index. 


397 


WEI 

Weighing  articles,  180 

Weights,  atomic,  42 

Weights  and  measures,  table  of  nu- 
merical data  of,  381 

Wiels's  process  for  coppering  cast-iron, 
204 

Wilde's  magneto-electric  machines,  347 

Wireing  articles,  325 

Wires  for  supporting  articles  in  vats,  171 

Wittstein's  process  for  analysing  silver- 
plating  solutions,  186 

Wollaston's  battery,  326 

—  first  electro-coats  silver  with  copper, 

Wood  engravings  copied   in  copper,  17, 


ZIN 

Woolrich.first  applies  magneto-electricity 
to  plating,  25 

—  's  silver-plating  solutions,  164 

Woolrich  and  Russell's  solution  for  de- 
positing cadmium,  274 

Workshop  arrangements,  313 

Wright's  first  employment  of  alkaline 
cyanides,  19 


V  INC,  79,  83,  86,  88,  274 
^     —  amalgamation  of,  332 

—  separation  from  copper  by  electrolysis, 
285  ^ 

—  estimation  of  by  electrolysis,  278 

—  selection  of,  for  batteries,  333 


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